Rumbling noise 2016 automatic?

This has been ongoing for a good couple of years. The car has had 2 mot's with nothing flagged and I have spent several days over the period trying to locate the source. I have had it in drive with the wheels in the air and using a bar as a stethoscope to get closer to the noise. It sounds really like a bad wheel bearing from the inside of the car but with the bar nothing in the rotating assembly is making anything like the same noise, there's the usual obligatory rotating noises as would be expected but they are all commensurate with the car running on stands. Pinion bearing nice and quiet, diff casing is just gears meshing, either end up near the wheels is both identical in tone and pitch and again suitably quiet. All bushings are in good order including the transfer box which is also just making normal gear and bearing noises.  If I didn't know that the bushings were good I would almost say that the shell is acting like a table when you put your phone on it playing music to be a simple amplifier, like something has bridged the nvh provision akin to having the transfer box hard mounted to the shell. None of the bearings have any play at all and neither test station rang the bell for anything else. 

Help!

Oh and the propshafts are not doing anything weird either, nice and smooth but no play.