Crown Vic clunking in the rear end
My '03 Crown Vic PI with 120k miles on it is starting to clunk and make metal to metal sounds. At first it sounded like the brakes were hitting the wear indicators, but they are new as of about 6 months ago. The sound only happened initially when in a turn, which leads me to believe the differential is the problem. Today it really didn't like backing out of a parking spot and starting forward. The motion seemed as if teeth are broke off and pieces lodged in between caused the car to struggle to start, until the pieces were free. There was a pretty good clunk and grinding associated with that.
I have had reccomendations to just replace the rear end. My options are to do it myself with new or junkyard parts, or have someone else do it with either type of parts. What is the reccomended route? I'm not exceedingly technical, so not sure how hard this is to do. I have heard the rear end is interchangeable with Mustangs and other Merc's, so finding the junkyard parts isn't too hard?
What would you expect this to cost at a shop?