Bakes squeak

My dad has an 83 320i and when he brakes I can hear his right front break and back right break squeak. Why is it squeaking? He said he replaced the brake pads about 2 months ago.

hte likely causes: the replacement pad composition, try another quality but not 'high-performance' brand & make sure the teflon or stainless steel pad shims are still there. if you look at the caliper piston to pad mating surface, you note that theres a notch 'missing' from about 130 degrees in it. this MUST be correctly oriented and sometimes get turned during brake work.