1995 brake problem

my 1995 grand am se 4 door has 4 wheel abs with drums in the back. i began to notice a real high pitch squeeking sound a while ago and thought nothing of it. then recently, when i first start going my rear right brake will lock up under even slight braking. i checked the pads and drum and all seems to be ok. i was wondering if ne one knew what was wrong.

Check to see that the parking brake is not partially engaged

I also have had this prob and the parking brake is not engaged. Same car except mine is a GT. It is a real annoyance but funny to see someone experience it for the first time

take the drums apart, and use brake cleaner to clean all the dust and cr@p off all the brake parts, reassemble and bleed your brakes. See if it helps :)