A few years ago i I as chasing down a vibration like yours. Turned out to be the AC compressor.

Did it get worse with the AC on? I'm guessing it did. How did you pin it down to the compressor?

It was by accident. I was on the driveway and the engine was idling. The dog was on the front seat and when I went to chuck her in the back my right foot accidentally pressed fully down on the accelerator pedal. The vibration / drone was really apparent at full throttle.
I was always under the impression that it was from the drive train..
After that it was a process of elimination and the first thing I did was turn the climate control off. Hey presto, no vibration..