Weird Noise Under The Car..

[swanvesta]

hi, i came back from a 70 mile trip last night and there was a strange din din din sort of noise coming from what sounded like under the drivers side just behind the front wheel. it wasn't a rattle or a clonk, but like a noisy hum with a gentle banging that increases with rpm's!!! WTF? any suggestions?

[Angelic0-]

Ever had a bad exhaust gasket, and it didn't sound like that ?

Valve adjustment required or something

[Henri]

Catalytic converter (catalyst) maybe... Had mine changed on warranty a month ago... if that is your problem, keep in mind BMW offers warranty for 7 years on this really expensive part.

Edit: when the parts inside this are broken, you'll hear a really annoying sound, louder when you raise RPM. Usually catalytic converter don't break before 200k + km, except if you bumped on a big fu.... hole and hit it, just like I did ;-)