A4 Vibration Noise
I was getting a vibration/rattle noise that sounded like it was coming from the transmission. It would happen from a dead stop to about 20 mph.
After looking around under the car I saw a round metal plug on the bottom of the bell housing (i think it allows acces to the torque converter). This plug is friction fit, but was very loose on my car. I poped it out bent the tabs out a little and reinstalled it and the noise is gone. Just thought I would post this in case someone else was trying to chase down the same problem. This noise was driving me mad for about 3 weeks.