So, I just recently bought a 2000 A4 Avant 1.8T. This thing has the "tiptronic" style transmission and about 140,000 miles on the odometer. I'm not sure when it started, but under medium to heavy acceleration there is a loud clunking sound that seems to come from right under the drivers seat. This only occurs from 3000-4000 RPM in 1st gear. Does anyone have an idea as to what might be causing this, or what I can do about it? Thanks!

 

Possibly motor or transmission mounts.