I can tell you what I went through not too long ago. Same problem. I dont believe it has anything to do with yer rock rail install. Mine rubbed for awhile, then suddenly didnt for awhile, THEN, my drivers side mounts through bolt snapped because the rubber was totally gone, and dropped the engine entirely while I was out wheeling, causing my front dshaft to contact the crossmember, chewing the hell out of all of my U-joints, ripping the tranny mount in half, and dinging the crap out of the underside of my ThumperXJ. I was stuck in the mud, out on the trail, and had about fifteen minutes of daylight left. I had to use a trailer hitch shank for a brace to get back to the road, which was murder, and completely finished off my U joints. I made the road, and luckily the broken, sloppy joints held long enough. Thumper then got a ride on the big flatbed wrecker back to my lab, where I had to replace ALL the U-joints, the top yoke on the rear d shaft, and both motor mounts(I installed the MORE bombproof rubber mounts, RE extended yoke and another stock tranny mount) CHECK THOSE MOUNTS! When it happened, I was, well, driving it like I stole it, cause I was in the mud. The horror..... The absolute HORROR!
