Had this happen several times to me, real stupid and easy to check, dust cover on the rotors. There's a stamped steel cover on the inside of the hub and mine must be slightly warped or something as it has occasionally (most often when I take a wheel off to perform some job) bent up so it was contacting the rotor as I drove. It has always taken a simple bend out of the way with a flathead or pair of pliers and problem solved. Just a possible check.