It has to be the wheel shroud (metal shield) rubbing. Sometimes they get bent. When this happens they make a grinding sound that sounds terrible rubbing against the rotor. An easy fix at any repair shop. Cost about $20.00. It happened to mine. Although I caused it when removing my rotor. I thought it was something pretty serious because of the metallic grinding noise. Also when spacers are used with aftermarket wheels and the new lugnut is to long it will go through and rub or damage the emergency brake.