Driving to work this morning. I noticed an awful groaning coming from the back of my mini when I am slowly rolling. It goes away at any amount of speed and isn't a constant sort of occsilates (sp). It kind of starts when I first when I let off my brakes after coming to a stop and rolling forward. I have no idea what this noise is but it scares the hell out of me ..

anyone have any ideas where I should look first ? Maybe rotors ?

 

warped rotor? brake piston(s) not fully releasing and rubbing? rear bearings?