The scary part was I actually had techs tell me that a wheel bearing needed to be replaced, and then I just walk up to the car, pull a huge rock out of the tread and tell them to test drive the car again. Low and behold, the "wheel bearing" is fixed!
Have you taken the brakes off yet? It could be a small piece of metal sticking off the rotor and catching on the backing plate. Or it could be the pad's wear indicator catching on the rotor. It could be a wheel bearing. . . more info needed.