Outside of what has allready been mentioned you can do the old brake burndown test.
Just run your bolt a a steady 45 mph with you foot firmly on the brakes and look for smoke. If they smoke replace them and turn drums and or rotors. A joke just a joke.
Common causes for brake squeal; oil or fluid on the drum or shoe, a fine powder build up inside the drum, or glazed drum or rotor surfaces.

I didn't do it, no one saw me do it, you can't prove anything! "Bart Simpson"