Brake lining wear indicator, ("squeaker") is rubbing on the rotor, (they usually stop making noise when the brakes are applied lightly), linings are worn down and the backing plates are grinding metal-on-metal, metal splash shield is bent and rubbing on the back side of the rotor, pebble stuck behind the splash shield.
October, 23, 2012 AT 2:17 AM
Also, high-pitched light squeaking is very common with the newer high-quality linings. The noise will be worse when they're still cold and in humid conditions. A brake inspection will determine how much lining is left by percentage, not mileage.