Loud exhaust: roaring, blowing or rattling underneath

The exhaust system works under high heat, moisture and vibration, so over time it burns through and works loose. A loud roar from under the front of the car often means a blown flex pipe, while a metallic rattle usually means a loose heat shield or mounting. The fault is easy to spot on a lift: we replace the flex pipe and weld up holes and mountings.

How it shows up

• The exhaust is noticeably louder, especially when accelerating
• A roar or tractor-like sound from under the front of the car
• A metallic rattle underneath at idle or at certain revs
• The exhaust pipe knocks against the underbody over bumps
• Exhaust fumes smell inside the cabin
• Visible holes, rust or soot on pipes and joints

Possible causes

1. 01

   Blown or torn flex pipe

   The flex pipe absorbs engine movement and cracks or burns through over time. The sound gets loud and boomy, especially under acceleration. The flex section is cut out and a new one is welded in.

2. 02

   Blown gaskets and joints

   Gas escaping at the manifold, downpipe or flange joints causes a ticking or puffing sound, especially when the engine is cold.

3. 03

   Loose heat shield

   Thin metal shields above the pipes rust at their mountings and rattle at idle or at certain revs. Usually fixed by securing or welding.

4. 04

   Broken rubber hangers and brackets

   When a hanger breaks, the pipe sags and knocks against the floor or subframe. The extra stress can crack other parts of the system.

5. 05

   Rusted-through silencer or resonator

   Rust eats through the casing from the inside, causing a loud noise at the rear. Depending on condition, a patch, a welded-in section or a replacement part is possible.

6. 06

   Damaged catalytic converter

   A broken-up catalyst core can rattle inside the housing when revving. This is often linked to engine problems, so it’s worth checking for fault codes too.

How we check

1. 01We listen to the engine at idle and while revving to locate the noise
2. 02On a lift we inspect the whole exhaust: flex pipe, joints, hangers, heat shields
3. 03We explain where the fault is and suggest an option: flex pipe replacement, welding, securing
4. 04We agree on the cost after the inspection and before starting work