[Max777]

I've had a simmilar problem for like the past year and still cant figure out what it is...

I replaced my u-joints and still had the problem.

The funny thing is, the vibration originally came up when I installed urethane mounts on my engine and transmission, but I also clutch in when the car is rolling and the vibration is still there.

From what I heard, the diff tends to whine really loud instead of vibrating, and the CV joints are usually not the problem if the boots are still intact. I was told to check the rear diff mounts, and found that one of my toe links (the long stick with two ball joints on it) was loose. I tightened that up and the vibration was still there, but it seemed to change a bit.