Vibrations of the brake pads resulting in a high-pitched sound are what causes brake squeal.  The vibration happens when the pads aren’t insulated properly from the caliper.  The factory equips brake pads with clips, insulator shims, and even a backing made out of silicone that keeps the pad glued to the caliper.  This prevents vibrating.

Often times brake squeal happens when brake pads become too hard.  These surfaces that are hard and smooth rub together and produce a noise similar to nails on a blackboard.  If this is what is happening, you need to resurface your rotors and replace pads.  This should eliminate squealing.

Also, brake rotors should be resurfaced when brakes are being done.  If they aren’t, squealing will result.  If brake pads are being replaced, resurfacing of rotors should be done with a finish that is non-directional.  This will ensure that brake pads will break in correctly.

When you hear brake squealing, act immediately.  Take your vehicle to a trained technician to ensure that your brakes are treated correctly.  Make sure that you have an auto warranty to cover any repairs that you have done.  You don’t want to end up paying more than you have to.