The u-joints have always had a little bit of slop in them (at least since I got this car in the mid 1990s) but that has ever only manifested as a clunk when I put it in reverse and never got worse over the years...It's a very different sound.
Well, I guess you can just ignore them, lol. When they get dry, they can an do chirp occasionally. The "clunk" that you are having is probably the notorious Chrysler clunk, that is commonly found in a 7 1/4 rear.
