Why is My Car Making a Rattling Noise When at Idle?

by Jennifer Porterfield | Last Updated: July 9, 2021
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Whenever you hear your car making a rattling noise when at idle it is always a gamble. A 50/50 chance of either being a simple fix or an expensive replacement. Because of this, hearing your favorite mode of transport make a noise you’re unfamiliar with is frustrating to almost everyone. The frustration may well be worse if it is a new car. To avoid frustration, today you’ll learn how to check for the problem yourself.

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What is idle?

You may notice that your car doesn’t make a rattling noise, or any other bad noise at all when going at any decent speed. The rattling may only occur when you are idling and then disappear once you reach a high speed. So what exactly is idling?

The meaning of idle is that your car’s engine is running while the vehicle is not in motion. Once the key has been turned, or a button pressed if you have one of those cars, and the ignition is switched on.

What the ignition does is generates a very high voltage from the car’s battery so that it can send the voltage to each individual sparkplug. This, in turn, ignites the fuel-air mixture in the combustion chambers using a spark plug that gets the engine running so you are ready to drive. Thankfully the cylinder wall stops any of the unburned gases from being released.

What is a rattling sound?

There are so many different noises a car can produce, so to make sure you’re efficiently researching anything, it’s best to know exactly what noise to listen out for.

Rattling itself is a series of knocking sounds. For instance, if you were to put a rock in a tin can and shake it, that would be somewhat similar to the noise you’re listening out for. Take this with a grain of salt, though, as rattling noises all depend on what item is knocking into what. This means that if a rubber item was knocking against something metal, it would still rattle but it would make a different sound than two metal items knocking into each other would.

What causes rattling while idling?

While your car is idle and produces a rattling noise, a few different things could be wrong. They will be spoken about more comprehensibly, soon. The most common types of rattling are from under your car or in your engine, so listen carefully to make sure you know exactly where the noise is coming from.

Rattling from under your car

When the rattle noise is located from under your car, it typically tends to be because something is loose. This can be a multitude of different things so it is best to lift your car from the ground using a jack so that you have enough room to go under there and locate the issue. If you can comfortably fit under your car then this is not necessary.

How to safely lift your car using a jack

Older cars come with a jack stored somewhere, however, newer cars do not do this as often. To locate a jack, use your owner’s manual from your car to see if one is stored anywhere. If not, buying one is the alternative.

Requirements
  • A car jack
  • Owners manual (located in the glove box/glove compartment)
  • Screwdriver (possibly)
Step one – preparing

Make sure that your car is on a flat surface and has the parking brake engaged. If you have a manual transmission make sure it is in neutral, for automatic transmission cars put them in park. Also, be wary of traffic and make sure you have read your owner’s manual so you know where to place the jack. Improper use of this can cause serious injury.

Step two – stabilize the vehicle

While the parking brake may be on, safety is still important. Using some bricks or a sturdy piece of wood, wedge them in front and behind the wheel diagonal from the wheel you shall be jacking. If you have more items, then feel free to block the wheel on the same side as the jacked wheel. This will ensure that even if your parking brake fails, your car will not move.

Step three – locate the jack point

Using the owner’s manual, locate the jack point near the wheel of your choosing. Make sure to double-check the manual so that you are in the correct spot and have placed the jack correctly. It goes without saying, never get under a vehicle that is raised solely by a jack. A solution to this is making sure you also have a jack stand. While they do not raise the car, they provide a stable and strong hold on the car that is used to prevent any injury should the jack fail. Jack stands are by far the most overlooked piece of safety equipment in any DIY garage environment. Once jacked to your desired height, place the stand underneath and raise it.

Step four – dismantling

When you need to remove both the jack and the jack stand, make sure to be very careful. You don’t want to injure yourself on the last step. Raise the jack a small amount until the stand is no longer holding the weight of the car, it is now safe to take out from underneath.

As for the jack, make sure you’re in a safe position so that the car may lower without you getting injured. Lower the jack until it no longer supports any weight and then remove it from under your car.

What to look for?

Exhaust system and heat shields

More often than not a rattling noise is linked to the exhaust system of your car. While looking at the exhaust system you may see a braided steel cover on your exhaust pipe, more commonly the exhaust Flexi pipe. Due to how hot it gets, the connections may have been damaged and loosened themselves. A way to stop the rattling is to locate the damaged steel bands that were holding the cover in place and remove them. This can be done with some heavy-duty cutters. Once the bands have been removed, the rattling should stop. However, this leaves the issue of the Flexi cover being loose. To rectify this temporarily you can either cut the braided steel mesh off or secure it using hose clamps.

The steel mesh is quite expensive to replace or secure using the proper items and a mechanic so the DIY alternative is much better for those who cannot afford it for now. However, it is still recommended that you eventually get it properly fixed via a mechanic as this ensures the safety of your vehicle.

Another common issue from underneath the car is a heat shield being loose. The screws may have rotted away on your heat shield so that it is flapping around ever so slightly. To repair this, simply replace the screws and use a screwdriver to tighten them. Ensure the rest of the heat shields are also secure by moving them slightly. If hit, they will produce a sound but that is natural.

If any of these issues persist, it is likely they will be noticed the next time you visit a mechanic or have a smog test. To properly understand an exhaust leak and how to identify it, you can read this article.

If your exhaust systems muffler is the issue then help can be found here.

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Engine rattling

To access the engine you need to prop up the hood using one or two hood struts that your vehicle may own. If your car has two hood struts then it is crucial they are being used at the same time to ensure safety. Engines are incredibly complex and need to be operating perfectly to perform as expected. Engines have a lot of different moving parts and these engine parts may overwhelm you, using a phone or camera take pictures of anything you’re about to remove so that you know how to put it back properly. If you’re seeking more information on engine rattling then this article is for you

Oil

If your engine oil level is too low it may produce an audible rattle capable of being heard over your typical engine noise. It is the most common thing to suspect when the engine is rattling. While it may sound like extra oil is the simple solution, an oil change is actually what’s needed. This is because oil is used as a lubricant and if the engine has gone unlubricated for a while then it may have caused a small amount of surface damage. Drain the oil at home, using an online guide, or get a mechanic to do it. Once the new oil has been added, if the rattling issue persists then it may be something else.

Serpentine belt tensioner

This device holds tension on the serpentine belt and if damaged may cause a rattling sound. The only fix for this is to replace it, which is easy enough to do at home. The replacement will cost you around $50 while getting a mechanic to do this may cost anywhere above $100.

Timing belt tensioner

The timing belt tensioner is used to keep tension on the timing belt. This is because the timing belt will be exposed to a lot of heat and will naturally expand over time, becoming looser and looser. The job of the tensioner is to counter this by increasing tension whenever there is a lack of it. To see if this is the rattling issue, remove the belt by moving the tensioner in the required direction to loosen the belt.

Once loose enough, remove the belt. You can now turn on the engine to see if the noise is still there. If so, you may need to replace the tensioner. Removing this belt and running the engine will simply not charge the battery and is safe to do so for a little while, but do not prolong this more than needed.

To replace the belt tensioner, it is best to visit a mechanic as the issue is quite complex for any DIY mechanic. It will have expensive repair costs but you should be able to ask for an instant quote to see if it would be cheaper elsewhere.

Wheels rattling

While this issue is less likely when you’re idle, it is still worth talking about. Your wheels, or components of them, may produce rattling sounds from either general damage or from any road debris potentially damaging them.

The first thing to check is your brake pads. Being the most crucial part of the wheel aside from the tire, it is best to make sure they are tightly connected and not at all loose. If they are damaged and that is creating a rattling noise, then replacing them with new brake pads is a must. Another thing to check would be your front suspension to see if that is the cause of your problems.

Another issue may be the way your wheels are connected to the car. To check this, locate all the lug nuts and connectors and ensure they are tightened fully. If the rattling persists then it is best to take the car to a mechanic.

Always make sure to test your brakes whenever you have touched near the wheels as your brakes are important. To check your brakes are working, drive as slow as possible and press down on the brake pedal. You should feel pressure on your leg and also feel the car stop. If not, apply no gas and roll to a gentle stop, and then engage the parking brake.

Interior rattling

If you are hearing interior rattling noises then the fix is most likely quite simple. Check around for any loose items, trash, or belongings of yours to see if they are causing the issue. Empty soda cans may rattle about when driving over a rough road. Your items stored in the glove box or door pockets may also hit against the sides causing a rattle-like noise

Why do it yourself?

Despite being a small rattling noise, some mechanics would charge a very high upfront cost to compensate for the time they spent looking for it. Some people believe that mechanics will then purposely look for other things to charge you for. Personal opinions aside, if you can go to the mechanic and tell them the exact cause of the issue then it will save them time and save you money. Instead of asking a mechanic ‘why is my car making a rattling noise when at idle?’ you can instead tell them the issue and feel confident that you know more about your car.

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Reduce sound

The sounds from a car can be very useful to understand if the car is working properly or not. However, there are some external noises that you just cannot live with despite not being able to fix them. Some noises are natural and even getting a brand new car will not fix them.

Road noise is one of the most irritating noises to deal with when driving. It is the collective sound you’d expect to hear while driving near other cars. You can hear tires rolling, engines turning and cars braking. On top of this, you may also hear horns, trucks, and motorbikes. All of these things can add up to a very stressful noise that you would want to block. Thankfully you can purchase sound-deadening materials that can help reduce noise. You may also choose to purchase an acoustic windshield as the air that hits your car can be quite distracting and frustrating as well. Thankfully there are multiple ways to reduce road noise so that it does not bother you anymore.

FAQS

Why is my car making a rattling noise when idling?

The most common reasons for this are either something loose underneath or something loose or damaged in your engine. Make sure to check the entirety of your vehicle including the tires, engine valves, and any connecting rod that may be loose. The exhaust pipes and exhaust system may also be the culprit.

How do I stop my engine from rattling?

To stop your engine from rattling you must first locate the source of the rattle. This will most commonly be either oil or radiator related. To check this, an oil change may provide useful and a quick check that everything is tight and working will also help locate the problem. If this does not help, seeing a mechanic will be a efficient alternative.