Ya what? I thought your car was for sale?...
Aaaaanyway, jack your car up, and have a listen. Get someone to turn it on and off for you while you hunt around for the noise.
Engine/gearbox mounts.
Up pipe/dump pipe knocking.
Midsection of exhaust knocking on underside of car.
Turbo heat shield.

Check em all. It's free.

__________________
Signarape!