I think I found out already... the trans mount was just about completely gone..... stock rubber isolator was in pieces when I removed the crossmember so I think that is what was causing the banging around down there. I bought a new poly mount bushing to install. There was also this weird U-shaped "weight" on the end of the tailshaft and I was wondering if it serves any purpose?? It must be made of lead as it is really heavy.

On a side note, has anybody ever done the "cryogenic freezing" of parts?? I heard it may make some parts stronger by "aligning' the molecules somehow??? I have no knowledge of this space age PFM type stuff so I wonder if I should look into dipping my new input shaft in the deep freeze TBF