Rattling Under the Car When Driving – The Easy and Not So Easy Fixes!

When driving, a rattling noise under the car can be pretty embarrassing when pulling up to the traffic lights. Somehow, cars have the ability to produce annoying rattles and bangs at the most inappropriate time. 

The good news is that some possible problems are easy to repair, so establishing the cause and applying the correct fix will eliminate that annoying rattle in no time. In this article, you will find the easy-to-fix causes of that annoying rattle and how to fix each one. Some aren’t easy to fix and will probably be out of most people’s DIY repair expertise; these are also included in this article but best left to a mechanic to sort. 

The Easy-To-Fix Cause of a Rattle Under the Car When Driving

When I say these are easy to fix, I’ve categorized these repairs into basic tasks that you can carry out at home on the driveway with a few basic tools, a jack, and an axle stand to get underneath the car safely. 

Exhaust heat shield

Running the length of the exhaust tunnel and attached to the car’s underside above the exhaust is an aluminum heat shield; it comes in multiple sections connected with tiny screws or can be tack welded into place. As the bottom is open to the elements, the screws get wet, rust, and the heat shield becomes loose. Once corrosion sets in, the heat shield becomes brittle, and you will find a large hole around the screw. As you drive, the metal heat shield will rattle under the car.

A rattling exhaust heat shield is the most common cause of a rattle. I would say every other car that comes into the garage with an under-the-car rattle is found to have a loose heatshield.

Because the heat shield protects the underside of the car from getting too hot, it is best to keep the heat shield in place. Refit it with the old or new screw and a large penny washer. If you can’t find a penny washer big enough, you can cut open a Coke can or similar, make a washer/section big enough to cover the hole and drill a hole for the screw.

Some mechanics will advise you to remove the heat shield; however, you should be cautious. Certain exhaust parts, like the catalytic converter, can reach over 1000 degrees Fahrenheit. If the car’s underside becomes hot enough, the car’s internal carpet or debris could catch light.

Loose exhaust

The exhaust is suspended by rubber mountings attached to metal hangers. The rubbers become dry and break with age. Rubber mounts allow the exhaust to flex when the engine moves under acceleration and gear changes. When a rubber mount breaks, the exhaust can rattle because it can now touch the car’s underside, especially when driving over bumps in the road.

Replace the rubber hangers with new ones available from all motor factors. Even if you can’t get a like for like, another with similar hole spacings will work. Sometimes, new rubber hangers can be tricky to mount because they are so stiff. Spray some WD-40 on the holes in the rubbers and the metal hangers before pushing them into place. If WD-40 doesn’t work and they are still too stiff, use a set of water pump pliers and a lever bar to force the rubber onto the hangers.

Engine dirt shield loose

Most new cars and some older ones will have a plastic tray clipped into the vehicle’s underside directly below the engine to stop dirt and debris from getting caught in the engine, where it could cause damage. These plastic trays are a pain for mechanics; they get damaged very easily when taken off for repairs or driving, and road debris hits them. You may have seen other cars driving with these plastic shields flapping in the wind under the car. It isn’t a metal rattling noise but can be loud in the car.

Like the exhaust shield, it should remain in place if possible; it protects against other problems. Depending on the amount of plastic broken, you might need to drill the plastic dirt tray and affix it with cable ties. Make sure it is well supported. You can sometimes replace the shield. A new one will clip straight back into place, but usually, when the shield breaks, the plastic it mounts to also breaks, meaning you can’t fit a new one even if you wanted to. 

new muffler

The Hard-To-Fix Causes of a Rattling Noise Under the Car

These aren’t such easy fixes because they can’t necessarily be carried out at home without a mechanic’s proper tools or expertise.

Broken exhaust

Rubber mounts suspend the exhaust on metal hangers. These metal hangers are on the car and the exhaust; they rust and break with age or can get damaged when changing the exhaust. The exhaust can no longer be supported, so it rattles and bangs on the car’s underside as you drive

It is sometimes possible to repair the bracket on the underside of the car or the exhaust by welding it or using wire to temporarily re-fix it. However, where the exhaust is concerned, replacing it may be the only option if it’s particularly rusty.

Suspension problems

One common symptom of suspension problems is a rattling sound under the car. However, steering issues can also accompany this problem. Some possible culprits of the rattling noise include broken coil springs, worn ball joints, shock top mounts, and anti-roll bar linkages. 

If you suspect any of these components may cause your suspension rattle, it’s important to have them checked for broken components or excessive movement. If one of these components is damaged or has excessive movement in a ball joint, it will need replacing. 

Replacing coil springs and other suspension components can be dangerous and requires specialized equipment, such as coil spring compressors. Understanding how these tools work and the risks associated with disassembling suspension components without them is important. For your safety, I strongly advise that you have a mechanic perform any necessary repairs.

Failed catalytic converter

A catalytic converter contains a honeycomb of precious metals. The failure of the catalyst is usually due to over-fueling or under-fueling and not because of any fault in the catalytic converter itself. This failure causes the internals to break apart, giving you a rattling sound while driving. You can check if the internals of the catalytic converter are loose by tapping it when it’s cold. 

Unfortunately, there isn’t much you can do apart from replacing it. If you continue driving, the catalyst will break down further, leading to a clogged catalytic converter or the internals being forced out through the exhaust. This can cause the car to release the wrong emissions and make the engine management light appear on the dashboard. 

Although replacing the catalytic converter might seem simple enough, you often require an oxy-acetylene torch to warm the connecting bolts up to take them apart. You must also be careful not to damage the oxygen sensors when removing them from the catalytic converter and returning them to the new one. 

Timing chain rattle

Although not necessarily heard from under the car, worn timing chains can produce a rattling noise that can echo throughout the car. Although timing chains work the same way as a timing belt, they are constructed of metal, hence the metal rattling sound. 

The failure mode of timing chains is the rattling noise, which, if ignored, will eventually snap, and the engine will no longer run. The good news is that in most cars, when the timing chain breaks, although you can’t drive the car, the chain can be replaced, and away you go; no further, more serious repairs are required. 

Engine failure

Another possible cause of a rattling noise is a problem within the engine, usually the bearings. Bearings are lubricated by engine oil and work by supporting and encouraging rotating engine parts to do so smoothly. If the engine were to run low on oil, these are the types of problems that can occur

Sadly, once an engine rattle appears, you can do little to stop it; the damage will be permanent and worsen if not addressed.

Is It Safe to Drive With a Rattle Under the Car?

Depending on the problem, you may be able to drive your car safely. However, don’t assume that it’s safe just because the car is not causing immediate danger to you or further damage to itself, even if it rattles really badly. You must first identify the cause of the problem to determine if it’s safe to drive.

For instance, if the exhaust heatshield is loose, it won’t cause any further issues, and you can drive unless it breaks off completely, which can be hazardous for other drivers on the road. However, a suspension problem, such as a broken coil spring, is unsafe to drive with. The reason is that your car may suddenly pull you off to one side of the road if the broken spring gets trapped in the spring pan.

Bottom Line

When driving, a rattle under the car can be alarming; however, the most common cause for rattling is exhaust issues like a loose heat shield. These are simple items to repair without needing specialist tools or expensive parts. Simply re-fixing will solve the problem. 

The issue comes when a component like the suspension or engine is causing the rattle. In these cases, replacing it at home without the correct knowledge and tools is impossible, so you must have a mechanic repair this for you. 

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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