I did an A4 to M6 conversion and every since I've been able to drive it, I've had a vibration from 3500-4500. My engine is balanced and blue printed and unfortunately, I didn't do the swap until after the car was all back together. So, I had to have the clutch assembly zero balanced after the fact. The funny thing is, when I pull the transmission out, I don't get a vibration anymore. I have an ES tranny mount, which is going to transfer more vibrations than a stock mount, but shouldn't it be through out the entire rpm range? This vibration happens at that spot no matter if I have the clutch in sitting still or if I'm at WOT. I pulled the transmission out and found something interesting. The part that covers the main shaft is 1) discolored, like it got hot and 2) bent flat on top. I have pictures, but they came from a cell phone. I'm not sure if this was there when I got it or not. I need some help/suggestions regarding this vibration. Do you guys think I should pull the clutch assembly back out and have it rebalanced ($60 because I don't live anywhere near the guy that did it the first time) or just put it back together and run an LS1 mount (to kill some of the vibrations). The vibration acts like an unbalanced tire; smooth except at a certain speed. Clutch assmembly or the motor?? Harmonics can be a bitch. Sorry for such a long post.