I have been worrying about this clunk-clunk coming from the rear as I take off from a dead stop. I was just able a look inside the glove box (long story involving a mirror and flashlight) and found that the 12 bolt is posi and was wondering if the posi engaging could be that sound? I don't know anything about posi-trac, but it seems to clunk and then catch, and proceed smoothly from there. This is in a '72 K5, 12 bolt, 3.73. Someone ease my mind.