Super tuning car runs good shooting for great

Wow, pretty easy to hear it there!
I have heard that before. But I gotta think.
It's only noisy when the engine is working, and it does not sound internal to the engine. And you're sure it's not a header banging on something. And to me it sorta sounds like it might be coming from the bellhouse area.

Ok it's coming to me.
One time I had a thrust bearing go out on me. Also an automatic car. Eventually there was so much play that the crank was moving so far forward under power that the TC boltheads were slamming into the back of the block, and machining it. But the bolt heads were cutting right through the boss for the tin-plug that seals the back of the cam-tunnel. And it was cutting the tin.
I think I would check your cranks end play.You may have to remove the TC access cover to pry the crank rearward. Or perhaps you can push the balancer backwards by placing a pry-block at the K-member. Prying it forwards is easy, just don't bust the timing-chain cover! If you pull that cover, you can inspect the block for the tell-tale machining going on right where the TC bolts pass by it. If, that's IF this is your problem, you will also see it on the TC bolt heads.
>But it sure sounds like an OEM flexplate, where they crack thru one of the sorta triangular cut-outs. But a B&M doesn't have those.
Is there any chance that your TC retaining bolts are the wrong size for the flexplate? If they would be 3/8 in a 7/16 hole, then I suppose they could work loose.But since I've never seen that situation, I don't know what that would sound like.
And one more idea; the flex plate has an engine side and a transmission side ...right?