possibly the wheel bearings?

for quite a while now my car has been makin some weird noises...only in the rear, like a groaning. I thougth it might be the wheel wasnt tight enough...but it was. Then i thought it was rubbin and it wasnt. Could it be the shocks, or metal to metal rubbing(where?), or the wheel bearings?

Thnx Matt

I had a "grrrrrroooooaaaannnn...ppop!" noise that I thought was bearings, and it ended up being a twisted spring in the perch.

Just a thought.