metal on metal is going to leave a rub mark if its not just vibration passing through an uninsulated joint (LCA, UCA, strut rod, etc) By braking you are putting pressure on the disc (if you have a frozen 4 piston caliper piston, you are pushing the disk in or out with LOTS of force unevenly) on a drum, you are doing the same, applying a directional force on a rotating object so you may be looking at bearings. Hows your caliper mounting bolts? Loose can cause a mean shudder, sounds like a grind.