86 535i automatic. when its cold, and i accelerate slowly away, i get a vibration and a knocking sound, it sounds like its coming from the tunnel directly below the handbrake area. it also does it when i am slowing down, and get to about 5 mph. it is a distinct mechanical knocking, like something is actually hitting against something else. The odd thing is that once the car is fully warmed up, it goes away. Any thoughts? Thanks!