ok, so I got under it while the wife revved the engine and we are able to reproduce the vibration. Whether it was always all coming from this or not, I can guarantee that it's coming from the X-pipe resonator. Stick my screwdriver in the breather hole, and i can absorb the vibration. But there is no crack visible on the external shield. Something internal must have cracked.
So it looks like the only way to fix this is to cut the x-pipe off and replace it with a new one (not another cheap piece of crap from GM to break again). While I have a welder, I dont want to learn on my exhaust
Looks like it's off to a an exhaust shop to custom fab me up something.