[chuckies76ta]

Looks like the pulley is kinda wrecked. I had the same thing happen to my wife's 68 Firebird. Could hear this noise every time we started it, and I finally found it was the bolts that hold the pulley to balancer. I used blue loctite and was never a problem again. I used the blue loctite paste, not the liquid.
I sold a friend a complete engine and a year later he was in the process of pulling the engine out because of this strange noise. I meet with him and found the 4 bolts loose on the balance pulley. We loctite them in and has been fine since.
On our IA2 engine it have a 3 bolt ATI balancer. I used the stock steel pulley that I re-drilled for 3 hole mounting. It uses 3-3/8" bolts. I used the blue loctite paste on the Allen head bolts, and to date no issue. I keep an eye on them. Here could be another issue is that your bolts do not go the full length of the balance threads. I ordered specific length Allen head bolts for my balancer. You just have to watch the engine side of the balancer that the bolts do not protrude to far out the backside of the balancer. I found the longer bolt has more threaded area to apply blue lotite. Seemed to work for me.

If I were you I would go back to the steel pulley. Loctite them in and keep an eye on it. I have a friend who took his balancer to a machine shop and had the 5/16 bolts upgraded to 3/8" bolts. No issue after that. Use some grade 8 bolts in it also.