Brake noise come in all kinds of sounds. If you hear a squeak that stops when you hit the brake pedal it is most likely your brake wear indicators. These are a warning that your brakes are almost completely wore out. If you are hearing a loud grinding metal to metal type noise the chances are that you have lost your brake pad lining completely and are doing major damage to other parts of your braking system. A squeal noise that comes and goes most often after a rain or a damp morning is most likely a brake pad compound problem cheaper pads tend to makes noise but a squeal once in a while is not unusual. When in doubt have a certified shop take a look and put your mind at ease.