Rattle update!
I took my car in to the dealer. They did the TSB for the exhaust hanger. I drove away and....BZZZZZZZT! The rattle was still there.
I went back and told the service guy to look up any TSBs on the rattle, and went to tell the tech the bad news. He came out and I mentioned something about the bell housing. He said he's had that problem on the V10s (trucks) and would throw some foam tape in there and that would cure the problem
The service guy came back and handing me another TSB. This one wanted to DROP THE TRANSMISSION, and replace the bell housing shield and add some alignment pins and crap. I opted for the foam tape option first.
I saw the tech undo the bottom two bolts. He added some sort of foam tape strip in 2 places and bolted it back up, trimming the excess foam. He plucked the bell housing shield (before and after this procedure) and you could tell that the rattle was from there, and that it should be gone (after he was done).
Day 2 of driving reports NO rattle anymore. I've even saved weight by having a few less exhaust retainers.
It's the bell housing shield. That's the buzz rattle.