[mtrombi]

I have a 2002 A4 Quattro - with tiptronic and it recently started vibrating. It only seems to happen when I press on the gas pedal, if i take my foot off of the gas pedle the vibration goes away. It happens mostly at higher speeds or at least i can't notie it as much at lower speeds. I thought the vibration was due to a bad 1/2 axle (right front) so i replaced it. It seemed to fix the problem for a about 1/2 a day but the vibration has come back. I have also noticed that when I'm at a stop light, the car seems to have a slight vibration as well. If i put the car into nuetral the vibration stops or goes away. Does anyone have any idea what might cause this?
Please help.