It is not just the annoyance of the vibration or even the risk of grenading a u-joint on the road that I would be worried about (although, that is pretty high on my list). It is the expensive things that vibrating driveshaft is attached to, namely the transmission and the rear axle that I would be worried about. Vibrations will eventually take their toll on bearings and gears. I would rather spring for a few shims and new u-joints than have to work on the tranny or rear axle AND then fix the vibration.

Michael