As i have told you guys before, my car feels like its going over rumble strips whenever the tranny is in use, (accelerating), then when the tranny has no tension on it, the noise stops. At first I thought that this was the mounts on the transmission, but they are brand new. Then I noticed this: The pic is labled to what they connect to.

http://www.PhotoCrib.net/is.php?i=2213&img=Bimmer_part.JPG

http://www.PhotoCrib.net/is.php?i=2233&img=bimmer_part_2.JPG

There is a small dent on the catalytic converter, not seen in this pic, that looks fresh, and is in about the same region as the noise. Any ideas?

If that crack is allowing things to move, something may be hitting the cat when the car is under load. You may need to get under there with the car running on jack stands and see what is happening.

Disclaimer: this is dangerous. If you die, don't blame me.