The rear brake discs rust which swell & catch on the back plate lip, easy repair....... Chock the front wheels up, jack up & remove the wheels, brake calipers, release the hand brake & remove the brake discs, look careful at the lip & you'll see where its catching on the lip. easy way is scrap the rust out of the discs. Hope this helps...
& to add, i found today that the rear shoe spring clip is catching on the studs in the hub & making a metal noise too.