Exhaust Flex Pipe

It is usually braided metal. It sits near the engine. It prevents cracks in rigid parts. Welding in a new flex section is often cheaper than replacing a whole pipe assembly. Because it is close to the engine, a leaking flex pipe can let exhaust reach the engine bay and sometimes the cabin ventilation intake. A rattling heat shield nearby is sometimes mistaken for a broken flex pipe.

The flexible section allows the engine to move on its mounts.

A broken flex pipe causes noise and leaks. Worn engine mounts accelerate wear.