I've had this happen twice on the pass side with my 96 (mfd' Jan 96) the original motor mounts dont look worn, but......they flex like crazy, I suspect a bolt worked loose and the combination of a very long weekend of wheeling, some in deep sand/mud, I felt some vibration then.... going over a rail crossing a little fast finished them the first time, the second time, I know that i hit a pothole way too fast ,(duh) I replaced the flexy stock mounts with More's new style mounts,(softer rubber) so far, so good. I was told emphatically by several techs NOT to use grade 8 bolts in that spot, because of their location, and what a pain they are to remove, and how hard it would be to get a grade 8 bolt drilled out to replace it.....Hadnt thought about the shear forces, but that is just another very good reason not to use grade 8 bolts. I saw a couple of friends xj's - they swapped in zj mounts, they are much better, even though I don't know much else about the mod, I suspect it couldnt be too hard to figure it out.