Rattling Noise When Accelerating: What’s Causing It?

Rattling Noise When Accelerating: What’s Causing It?

It can be quite unnerving when your car makes a rattling noise when accelerating. Since your car isn’t supposed to make any noise other than engine, exhaust, and tire noise, it would be wise to check what’s causing it. The problem can be as simple as low engine oil levels, but it may be something more serious as well. We’ll discuss the possible causes in this post, as well as the repair costs you may have to face when your car makes a rattling noise when accelerating.

Rattling Noise When Accelerating Possible Causes: If It’s Coming from the Engine

The car is a complex piece of machinery, and a lot of things can go wrong with it. Diagnosing a rattling noise may take some time and patience, so bear with us. Ideally, you should try to identify where the rattling noise is coming from. If it’s coming from the engine, here are some things that might be wrong with it:

Low Engine Oil Level

It can be as simple as not enough oil circulating through the engine. When was the last time you had an oil change? When was the last time you checked the engine oil level? Low engine oil level means your engine isn’t getting enough oil and isn’t properly lubricated. Without proper lubrication, friction will increase between the engine’s internal components. This can result in rattling noises coming from the engine when accelerating.

Not only that, low engine oil levels can result in other problems as well. Such as loss of performance and overheating, and the latter can result in permanent engine damage. So, it’s best to check your engine’s oil immediately, especially if it’s been a while since you last had an oil change.

To check this, simply locate your car’s engine oil dipstick. Pull it out, and then wipe it with a rag. Afterward, reinsert the dipstick and pull it out again and see the indicators on the dipstick. It will have a minimum and maximum level indicator on it. You should also check the oil’s color, if it’s black and thick, then you will need to do an oil change. This means the engine oil is old, and won’t be as efficient in lubricating the engine. Most cars will need an oil change between 3,000 to 7,000 miles, but some cars with synthetic oil may go as far as 15,000 miles before needing an oil change.

Timing Belt Or Chain Tensioner

An engine has what’s is known as a timing belt or chain. This belt or chain guides your engine’s crankshaft and camshaft on what to do, to make sure the components inside are moving and working smoothly. The belt or chain system has a tensioner that keeps it snug, centered, and makes sure the belt has steady tension as it needs tension to operate properly.

If the tensioner loses strength, then the belt or chain will become loose. When there’s slack on the belt or chain, this will throw off the engine’s timing and some parts may hit against one another, such as the valve guides. Obviously, this will result in rattling noises coming from the engine. A loose belt may also make a squeaking noise. If this happens, you will need to replace the tensioner, and possibly the timing belt or chain as well.

Checking the timing belt tensioner can be tricky since you need to remove the timing belt cover. Some engine accessories and the harmonic balancer might be in the way too, so you’ll need to remove them first as well. If you can gain access to the tensioner, press the timing belt between the pulleys. It should move no more than about 1/4 inch, if you don’t feel a lot of tension, then it’s probably time for a new tensioner and possibly a new timing belt or chain (with some guidance on when to change the timing belt).

Bad Engine Mounts

The engine mounts are what connect the engine to the car’s chassis and secure it in place. These mounts are made of metal and rubber, and they will usually last around 5 – 1o years, but they often last longer than that. However, they will wear out over time, and when they do, your car’s engine can move around in the engine bay. This means the engine can come into contact with the chassis, causing rattling noises coming from the engine bay.

Also, engine mounts have a dampening effect that reduces vibration coming from the engine. Because of this, when the engine mounts go bad you will also feel your car vibrating excessively. To find out if you have a bad engine mount, you’ll need someone to get in the car whilst you take a look at the engine. Have them put the car from Park to Drive, and then from Drive to Reverse. If you see the engine moving excessively, then you likely have a bad engine mount.

You can also take a look at the mounts to see if they’ve gone bad, but this can be hard to find out unless you know what you’re looking for.

Piston Slap

Another possible issue you might be looking at is a piston slap. The engine’s pistons sit snuggly inside the cylinder and they go up and down as the engine is operating, and they require very little side-to-side movements. Over time, the engine’s piston and cylinder may wear down due to heat and friction. When they do, there will be more room between them, causing the piston to rock and slapping the cylinder’s wall. This is what’s known as a piston slap and causes the rattling noise you’re hearing.

This sound usually happens when the engine is still cold and you immediately drive away, as the components contracted in the cold and haven’t expanded because the engine is still cold. Once the engine gets to operating temperature, this noise should go away on its own. In fact, it’s perfectly normal for some performance cars to experience this due to their engine’s design. Some of these cars include the Nissan GT-R and certain Corvette engines.

However, if the piston slap persists even at operating temperature, then this is a cause for concern. Especially if it’s accompanied by other symptoms such as blue exhaust smoke and rapid oil loss. This is because a consistent piston slap can wear down the piston rings, allowing oil to enter the cylinders and get burnt with the fuel. We wrote a comprehensive guide about piston slap and you can read about it here.

Rattling Noise When Accelerating: Other Possible Causes

If the rattling noise isn’t coming from the engine, there are some other components that may cause the noise. Here are the other possible causes you should look at:

Exhaust System Problems

The car’s exhaust system consists of several components, such as the catalytic converter, the muffler, and the exhaust pipes themselves. When one of these parts goes bad, it may make a rattling noise. For example, the catalytic converter is a device that filters the pollutants in the exhaust gas and makes it less toxic for the environment. Over time, their internal structure can break down and become loose, making a rattling noise when accelerating the car.

Rattling Noise When Accelerating

This can also happen to the muffler as it rusts away. Similar to the catalytic converter, components inside the muffler may break down and create a rattling noise when accelerating. Another possible cause is the exhaust hanger has disconnected. This results in an exhaust component hanging loosely from the car, hitting other components or possibly the road whilst the car is moving.

If you’re sure the noise isn’t coming from the engine, take a look underneath your car and see if any exhaust components have come loose or have badly rusted. Other exhaust components you should check include the exhaust gasket and the pipe connections.

Bad Heat Shield

The car’s exhaust system can get very hot, with temperatures often reaching somewhere between 600°F to 930°F. Because of this, your car has heat shields in several spots to protect other components from the heat. Heat shields are usually made of carbon composite material and can withstand a great amount of heat.

Because they sit underneath the car and close to the ground, heat shields are also prone to debris and moisture, which can cause rust problems. These rust problems can eventually cause the heat shield to break free from the welds, causing them to rub and vibrate against other components. This then leads to the rattling noise you hear inside your car

Flywheel Or Flexplate Damage

Depending on the transmission you have in your car, it may have either a flywheel or a flexplate in the system. If you have a manual transmission, then your car has a flywheel. The flywheel attaches to the car’s crankshaft, that’s the shaft that sits at the bottom of the engine and is powered by the piston’s motion. The flywheel is there to smooth out the power delivery coming from the engine. It also stores energy from the engine, so it will keep spinning even though you’re not pressing the accelerator pedal. This prevents your engine from immediately stalling.

Meanwhile, if you have an automatic transmission with a torque converter, then your car has a flexplate. A flexplate is lighter than a flywheel, and it can flex forward and backward as the engine RPM increases due to fluid pressure inside the converter. But it serves the same purpose as the flywheel.

If the flywheel or flexplate has damage like cracks, it will bend as you accelerate because of the torque applied. The bending will misalign the gear teeth, causing the rattling and sometimes knocking noise as you accelerate. If the noise goes away when you take your foot off the gas, this is an indication that you have a flywheel/flexplate problem. This happens because when you let off the gas, less torque is applied and so the flywheel/flexplate comes back into its natural position.

Loose Interior Trims

The rattling noise you hear may be nothing more than a loose interior trim inside your car. Some loose nuts and bolts in the interior may also be the cause, and this is not uncommon especially for older cars. Try listening for the source of the rattling noise, and see if any interior trims are loose and shaking. If you see any, try securing them back in place and see if some nuts and bolts need tightening.

Some interior trims that may come loose include the door sills, glove compartment doors, center console lid, dashboard bezel, and the door components such as the latch assembly and lock cylinder. While you’re at it, check for loose change and other small items in the car. A couple of spare changes in a cup holder is enough to make that annoying rattling noise. All you need to do to get rid of the noise is put them somewhere more secure and clean your car’s interior.

Rattling Noise When Accelerating: Repair Cost Estimates

So, now you know what might be causing the rattling noises in your car. But what about the repair costs? How much will these potential problems cost you? Here are some estimates to give you an idea before you take your car in for repairs:

Rattling Noise When Accelerating: Low Engine Oil Level

If the rattling noise is due to low engine oil levels, then an oil change will do you good. An oil change is typically around $50 – $125 for most cars. But if your car uses synthetic oil then you might need to pay slightly more than that.

However, a low engine oil level might be an indication of a more serious problem in your car. If you just topped off your engine oil recently and it’s already low, then you likely have an oil leak. Most cars lose about a quart of oil every 1,500 miles, any more than that means you have a more serious issue at hand.

Check your car’s underside and see if any leaks are coming from the oil pan. If you notice a puddle of oil underneath the car, this usually means there’s a leak from the oil pan. An oil pan gasket will typically cost about $320 to replace including labor. If you need to replace the entire oil pan, that can run you anywhere between $200 – $500.

Rattling Noise When Accelerating

Another possible source of the leak is the head gasket. The head gasket is a component that connects the engine block to the cylinder head, and it prevents oil from leaking into the engine. If you see blue or thick white smoke coming from the exhaust pipes, this means your head gasket is blown and oil is getting burnt inside the engine, causing rapid oil drain. Replacing the head gasket can cost anywhere between $1,500 – $4,500.

The valve cover gasket may also wear out and leak oil out. If you see oil all over your engine bay, the valve cover gasket is likely to be the culprit. This can be a fire hazard, so best to fix it immediately.

Timing Belt/Chain Tensioner Replacement Cost

The timing belt/chain tensioner costs around $350 to replace on average. It’s a relatively simple job for a professional mechanic and should take no more than about an hour, which will cost you about $80 in labor cost. However, some cars may have more complex designs and require more disassembly to get to the tensioner. This means your mechanic will need more time to replace the tensioner, resulting in higher labor costs.

It’s possible to replace the tensioner yourself to save costs, but we don’t really recommend doing this unless you know what you’re doing.

Engine Mount Replacement

Engine mounts are not very expensive. They’re a simple component and usually cost about $50 – $150 each. For example, an engine mount for a 2015 Toyota Corolla is about $109 each. However, the labor cost varies depending on the complexity of the job, and it can cost anywhere between $200 – $450 in labor.

Also, keep in mind that you will often need to replace engine mounts in pairs. So, if your car has four engine mounts, and the front left mount has gone bad, you will at least need to replace both front mounts. This means you will need about $200 for a couple of mounts, and at least another $200 for labor. Assuming you need to replace four mounts and the labor cost is at $450, you’ll be paying at least $850 in total.

Replacing the engine mounts yourself might be a good option to save some money. But this is quite a complex job and we don’t recommend doing this yourself if you’re not sure about your mechanical skills. If you’re interested in knowing how to replace engine mounts, we recommend watching this video from ChrisFix:

Exhaust System Repairs

If the rattling noise when accelerating comes from your car’s exhaust system, then the repair cost will vary greatly depending on which components need repairing. A muffler or exhaust pipe repair will cost around $50 – $150 depending on the severity of the damage. If you need a muffler replacement, expect to pay somewhere between $250 – $450 including labor, depending on your car’s make and model.

Meanwhile, new exhaust pipes will cost somewhere around $650 – $750 including labor costs. But perhaps the most expensive repair of them all is the catalytic converter. If your catalytic converter is making a rattling noise, then you will need to replace it. This can cost from as low as $900 to as high as $2,400 including labor.

The reason why they’re so expensive is that they need to be made from a mixture of precious metals such as platinum, palladium, and rhodium (for more insight, check out our explainer on which catalytic converters have the most rhodium). They need these metals to perform their function, and hence why they’re expensive.

The good news is catalytic converters will usually last at least 10 years. But you need to make sure that your engine is healthy to prolong the life of the catalytic converter. Rich fuel mixture and oil leaks can result in more toxic gases. This causes the catalytic converter to work harder, leading to premature damage.

Heat Shield Replacement Cost

If the heat shield needs to be welded back in place, this should cost you around $100 in labor cost. But if you need a new heat shield altogether, this will cost somewhere between $250 – $400 depending on your car’s make and model.

Flywheel Or Flexplate Replacement Cost

This is also one of the pricier replacement jobs. If your car’s flywheel or flexplate has gone bad, then you will need to replace it. A flywheel/flexplate assembly is usually around $400 to purchase. But since your mechanic will need to disassemble the transmission to replace it, the labor cost can be quite high.

The total cost will depend on your car’s make and model since different cars have different flywheel/flexplate designs and complexity. But expect the total cost to be anywhere between $800 – $2,500. Most of the cost will come from the labor cost since your mechanic will need to tear the transmission apart and then put it back together after replacing the flywheel/flexplate.

Can You Drive With A Rattling Noise When Accelerating?

Unless the rattling noise is coming from a loose interior accessory, we recommend fixing the problem immediately. Even the smallest issue with the powertrain like not enough oil can lead to much more serious and expensive problems. Your car needs all of its components to run perfectly to work smoothly. If one of these components fails, it can affect other components and cost you more expensive repairs. Not exactly ideal if you want to keep your car for the long run.

If the repair cost is too high, consider selling your car as-is. In some scenarios, such as with a broken flywheel, this is essentially selling your car with a blown engine. Meaning you’ll have to sell your car at a much lower price than its market value. We recommend this when your car’s value is not far off from the repair costs.

Facts: Common Causes and Fixes for Rattling Noises When Accelerating

  • A rattling noise when accelerating can be caused by several issues, including worn-out suspension components, a misaligned driveshaft, broken or loose heat shields, and low transmission fluid.
  • These problems can result in uneven tire wear, a bumpy or noisy ride, or overheating and burning smells from the engine.
  • Worn-out wheel bearings can cause the tires to shake and wobble, while faulty exhaust components can cause rattling and corrosion damage from road debris.
  • Problems with the valve train, including worn-out intake and exhaust valves and faulty hydraulic lifters, can cause the engine to knock or make clicking noises.
  • Loose or faulty engine components, like drive belt pulleys and tensioners, can also cause rattling or squealing noises.
  • Low transmission fluid can cause the transmission to struggle to shift, overheat, or slip gears.
  • Fixing a rattling noise when accelerating depends on the root cause of the problem, and some fixes are simple, like tightening loose parts or topping off fluid levels.
  • Other fixes may require expertise, such as replacing damaged suspension components or realigning the driveshaft.
  • Securing a loose heat shield involves raising the car and tightening the screws connecting the shield to the vehicle or replacing the shield entirely.
  • Repairing the suspension system involves lifting the car, replacing any damaged components, and tightening all components to proper torque specifications, which may require a mechanic’s expertise.

Rattling Noise When Accelerating: Conclusion

Your car isn’t supposed to make any noise when you’re driving apart from the engine, exhaust, and tire noise. So, when you hear a rattling noise when accelerating, it can be rather unnerving. But hopefully, this post has helped you in figuring out what caused that noise. And gave you an idea of the repair costs that you might need to face to get the problem fixed.

Again, we remind you not to postpone any repairs if the rattling noise is caused by an engine or powertrain issue. The smallest problems can lead to severe damage that will cost thousands of dollars to repair.

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