A new rattle from underneath your car is almost always one of a small list of culprits. Most are cheap to fix once you've identified the source.
Top 7 culprits
1. **Loose heat shield** — tinny rattle at idle, worst when warm. £30–£90 to fix (often just a new clamp) 2. **Anti-roll bar drop link** — clonk over speed bumps. £80–£160 per side 3. **Exhaust bracket/rubber** — rattle on tickover. £30–£90 4. **Failed catalytic converter** — rattle that gets worse with revs. £300–£900 5. **Loose undertray fastener** — wind noise + rattle at speed. £15–£60 6. **Worn handbrake cable shoes (rear drums)** — rattle at low speed. £80–£180 7. **Worn engine mount** — clunk when going from drive to reverse. £180–£450
How to narrow it down
- At idle only → heat shield or exhaust bracket - Over bumps → drop link or undertray - Worse when warm → heat shield expanding - With revs → catalyst or exhaust - Pulling away → engine mount
Is a rattling heat shield dangerous? — No, but ignore it long enough and it falls off — annoying and potentially a road hazard.
Will rattles fail an MOT? — Loose exhausts, broken cats and worn drop links are MOT failures. Heat shield rattles aren't (unless the shield is hanging off).
Bob's Mechanical Repairs — independent family-run garage in Birnam, Dunkeld, Perthshire. Call 01350 727 276 or email bob@bobsmechanicalrepairs.co.uk.