So the working assumption is ‘drivetrain’ issue?
I’d start with the obvious - any loose bearings / mounts on the prop or rear diff?
If the CV joint was fubar, it would normally be noisy when making a full-lock turn left or right.
Did a underside check today, now when the winter is over. Propshaft carrier bearings still tight, diff doesn't move exessively, couple of rust spots haven't got any worse - nothing to worry. Then I remembered that I didn't replace the rubber...
3 glowplugs wqere replaced last year. The one in cylinder-2 is still stuck fast in the engine. But these should only impact starting, and not running whne engine is warm.
EGR black arrived & waiting for FIP & Regulator seals - these will be...
They are going down the IDM route on the fuelling side…
Re-reading your post, are you saying the symptoms are there under heavy engine power/revs, even if stationary?
It does sound ‘mechanical’ from your description, or perhaps the Haldex ‘scrabbling’, which is a known issue on the ecm and an easy fix. From your description of ‘strong physical jolt’, it might not be this, but it’s a very simple check you can...
Another day - another bump for free.
Maybe it might help if you said ‘where’ in the country you are / it is.
And perhaps a few pictures of underneath/arches, so peeps can see that apart from a snorkel and a winch, it’s not got general rust...