What causes brakes to squeak?

Answer 1

Excellent question. This is possibly the least understood of all car problems. Squeeky brakes, despite what you've heard or anyone may tell you, is not caused by the brake pads rubbing on the brake rotor. Instead, it is caused by the brake pads vibrating in their mounting clips on the caliper assembly. This can be caused by rust and corrosion or simply old age. If you wish to stop the squeeking, it may be necessary to replace the pads, but not always. Often you can use a compound called "disk brake quiet" or "stop squeel" (or something similar- you get the idea). Take the pads out, clean off any rust/dirt/grime, and coat the back of the pads with the compound anywhere they touch the caliper. Usually this will quiet them down.