rear axle locking up and popping

[lowrodderchev]

so my new daily driver slash toy is broken couples weeks back in the mountains was backing up and it kept locking up then a hard pop from the center cap wheel cover. we checked it out and everything seem fine. today i'm pulling into work and i hear it again and as i'm turning into a parking space the rear drivers wheel sounded like it was starting to drag then break loose and that loud pop happen again in the wheel cover. this is something new to me i put new u joints after the mountain incedent any ideas what it might be better yet how expensive its gonna be thanx guys