Doug, guess it *could* still be your rear ds. Maybe try this - throw some weight in the back, to change the angle. If your rumble changes tone, it could point to your rear ds? I'd be surprised if it was though, since they're so short... I woulda guessed ujoint, but you've eliminated that?

1991 HZJ77, 1999 KZJ90, 1999 UZJ100, 1992 M101CDN2
https://www.thegearheadproject.com/category/jdm-journeys/