Clicking noise in rear end...cv joint? diff? wheel bearing?

[bimmerboi318]

not a fun saturday night....

i noticed tonight a faint clunking from the rear of my ti tonight on decceleration. i didnt think much of it until it became louder. whenever i let off the gas, it sounds like someone is knocking on the underside of my car several times per second. i think its going the same speed as the driveshaft...but i could be wrong and it could match with the wheel speed. i've been told it could be a worn cv shaft, but im worried it might be a differential issue. i thought it might be a universal in my driveshaft, but it only does it under decel and there doesnt seem to be any driveability problems. no noticable vibrations, doesnt pull, etc...

if anyone has ANY info, please help me out here. im putting the car up on the lift tomorrow, but im a tad nervous about it. this is the first, not-so-good, noise i've heard from my car EVER.

thanks.