A rattle from underneath the car, often compared to the sound of a small object turning over in a clothes dryer, is one of the most common noise complaints. The good news is that in most cases, the cause is one of the cheaper repairs on this list. If the sound is a heavier, single thud rather than a metallic rattle, see our guide to a heavier knock over bumps — that's more likely suspension.
The most common causes
1. A loose heat shield (most common cause)
Heat shields are thin metal guards around the exhaust manifold, catalytic converter, and other hot components, protecting nearby wiring and fuel lines from excessive heat. Because they're thin metal exposed to road salt and moisture, they rust over time, and the mounting points can corrode or crack. A loose shield vibrates against the exhaust or nearby bodywork and produces a rattling sound, often most noticeable on acceleration or over bumps. If you're running a van daily, worth knowing how to plan a repair like this around your work rather than losing a morning to it.
2. Loose or failing exhaust mounts
The exhaust system is held in place by rubber mounts that isolate it from the car body and absorb vibration. If the sound is more of a single clunk felt through the car when you pull away or come on and off the throttle, it may instead be a worn engine or gearbox mount rather than the exhaust. When these perish or fail, sections of the exhaust can move more than they should and knock against the underside of the car.
3. A failing catalytic converter
Less common, but worth knowing about: if the internal structure of a catalytic converter breaks down, loose fragments inside can rattle, particularly at idle or when revving in neutral. This is a more expensive repair than a heat shield, so it's worth having a mechanic confirm the actual source rather than assuming the cheaper cause.
4. Loose bolts or fittings
Sometimes it really is as simple as a loose bolt or clip somewhere in the exhaust or underbody. Cheap and quick to fix once located, though pinpointing an intermittent rattle can take a bit of investigation.
Is it safe to keep driving?
Probably fine for nowA light, intermittent rattle with no change in exhaust noise or performance. Get it checked at your next convenient opportunity, ideally before an MOT.
Book it in soonA persistent rattle, especially if you can see a hanging or visibly loose component underneath. This is also a common MOT advisory or failure point.
Don't delayA rattle accompanied by a noticeably louder exhaust, a burning smell, or a visibly detached component. Get this checked promptly, as a dragging part can be a road hazard.
What it typically costs to fix in the UK
| Likely job | Typical UK cost |
|---|---|
| Heat shield re-securing or minor repair | £150 – £300 |
| Exhaust mount replacement | £50 – £150 |
| Exhaust section or backbox replacement | £150 – £500+ |
Ranges compiled from Bumper UK pricing guides, 2025-2026. Your actual quote depends on your specific vehicle and garage.
Frequently asked questions
Is it safe to drive with a rattling exhaust?
A rattling heat shield is usually not urgent, but a loose or hanging exhaust component can be a hazard if it detaches while driving, and can be an MOT failure. If the rattle is accompanied by a noticeably louder exhaust note, get it checked, since this can indicate a leak or hole.
Why does my exhaust only rattle at certain speeds?
A rattle that appears at specific engine speeds or under acceleration, then disappears, often points to a heat shield vibrating at a particular resonant frequency, or a loose part contacting another component only when the engine and exhaust move a certain amount. This changes with revs, road speed, and load, which is why it can seem intermittent.
How much does it cost to fix a rattling exhaust in the UK?
A loose heat shield that just needs re-securing or a minor repair typically costs £150 to £300. If a section needs full replacement or the rattle turns out to be a failing catalytic converter, costs can run considerably higher, so it's worth getting a proper diagnosis rather than assuming the cheapest cause.
For other noises, see all car noise guides.
Not sure what's causing it?
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Try MechdThis guide is for general information only and isn't a substitute for a qualified mechanic's inspection. A visibly loose or hanging exhaust component is a road hazard and should be checked promptly.