Never mind. Please move on. Nothing to see here.
I just spent some more time down there to check to see if the noise was coming from further forward in the tranny and not actually from the pan to indicate that it might be a flexplate issue and while down there I started smacking things with the heel of my palm and when I hit the exhaust pipe about 6 inches behind one of the cats, the rattle became worse. I thought I might have a catalytic failure issue similar to that of the GP, but upon further investigation and smacking, I discovered that the rattle is coming from the rear O2 sensor on the driver's side. No codes yet and it passed a smog test a few months back with flying colors (it was making the noises at that time), so I guess it still functions properly. I could have sworn I was feeling the rattle in the transmission pan, but maybe it was just all in my head.
2002 Chevy Suburban 1500, G-Oil 5W-30, Fram TG3506
2006 Pontiac Grand Prix GT, Castrol SynBlend 5W-30, Fram 3387A