Does anyone know what this might be???

I am building my 70 Dart with 383, 727, 8 3/4, and I'm at the point where exhaust is all on and I drove it around some today.

The issue is, I am getting a bit of starter noise just every once in a long while... I have no idea why??? Just driving around, and I'll get a bit of noise n then nothing...

I tried to sort of shim the starter (spacer) but no...

Is there some way maybe I need to tighten the torque strap a bit n the motor is moving n causing this? I am just guessing, NO IDEA...