Well that was fun. Scolman was on the right track. Didn't need a shim on the starter but I did need the solenoid return spring that was sitting on my workbench. I rebuilt the starter last week and seem to have forgotten it. The bendix wasn't pulling back far enough and was contacting the plate. Didn't look like it while it was running but I guess it doesn't take much. Please don't post this on the internet or anything I feel a bit foolish.