I have this weird nose coming from my exhaust?

[blink0r]

Ok, i'll make it short and sweet. Yesterday i noticed a loud vibrating sound coming from behind my rear left wheel.... which makes me think its my exhaust. It happens the most when the car is cold, or when i push in the clutch to shift gears. Any ideas what it might be? My only guess is my muffer?

[sykikchimp]

What kind of vibrating sound?  Metallic? do you hear it, and feel it?  does it occur at certain RPM's?  Give us some more specifics man.

charles