rear u-joint

Dave NEO said
seems to be clutch T.O. but am looking around for other causes

Dave NEO said
……. - more of a clutch related noise I can get w/o driveshaft spinning.......

So this is noise/vibration only while depressing the clutch pedal and engaging the plate fingers?

Dave NEO said
...….just to be clear - no play in joints at all -...….

IMO, Wear may be a little tough to see without actually opening it up. You could pull the four bolts, visual inspect the two that are open and "feel" the swivel of the two still in the driveshaft.