Rear end or brakes problem?

[NOT THE BLUE LAMPSHADE]

I have a 1991 Eagle Talon TSi AWD 5spd. Only mods are a 3" turbo back and the car's running 16PSI. I checked out everything in the rear end and it looks fine to me, but I'm not a guru on brakes or alignment or anything. I actually just picked it up from Ross (MATCHBX) on Friday. Anyway, I noticed on Sunday that the rear left wheel is missing a lug nut, in fact, there isn't a stud to screw one on. I know I need a hub assembly back there now. When I hit the brakes, an awful clunking and scraping sound comes on and the car jerks in that direction and actually dips down on that side. I don't care how much it costs to fix it, but before I bring it in I'd just like to know what you guys think it might be. I know where I can get a new rear end and axels for cheap so I might just go ahead and replace it anyway since a clicking noise comes about ONLY when you go in reverse over 5mph. Any help would be greatly appreciated, thanks.

Tom