1967 Chevy Camaro Starter Noisy When Hot

The starter when cold starts fine and without noise. After the car has been driven any length of time at all the starter will spin until it sounds like it hits something solid with a loud clang. If you keep trying to start it it will keep doing the same thing until it sits for 15-30 minutes then starts normal.

I have been told that since I run header without a heat sheild on the starter that could be the culprit.
Besides that I am at a loss.