I have a 01 2wd XJ and at around 1.5-2.5k rpm going around 50-60mph, there is a jolting coming from the rear of the car, seems like around the tranmission. I replaced the transmission mount and it didn’t fix the problem and the ujoints seem to have no slop in them when I shook the driveshaft. The jolting also happens if going over bumps at around the same speed or lower at similar rpm. I was wondering if anyone has any advice on this problem

 

Going over bumps? Something is loose and you should be able to move it. try here.