Some brake noises are normal. Others can indicate problems. In general, any brake noise that persists for some time warrant a trip to the service department. Here are some sounds — good and bad — that are generally charactersitic of all brake systems.
Grinding
Grinding due to rust build-up on the rotors is of little concerns. The build-up usually can be knocked off, sometimes it disappears after a few stops. However, if grinding persists, there could be a more serious problem with the rotors or pads, and you should head straight to the service department.
Loud squeal
Disc brakes with wear indicators may produce noise that indicates it's time to change the pads.
Trace squeak or squeal
Semi-metallic brake linings sometimes emit such a sound. Rain, humidity or cold brakes in the morning also could be the source. If the problem persists, have it checked out.
Clicking
Sometimes accompanied by a slight pulsing in the brake pedal at low speeds, this is most likely the anti-lock braking system performing a harmless self-check.
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