Michael, yes it could be the propshaft but at least on my 4/4 the propshaft only touches the transmitting tunnel under hard acceleration in first and second gear and when loaded with two people and a full tank.The Plus4 offers some more torque and could be involved easier.
I have to watch it. Did some fast accelerations
but as far as I remember it was not linked to that.
I have no knowledge about a standard Plus4 if she has anti tramp bars etc.
I don't think so.
But what you describe sounds to me more like the leaf springs could make the sound and touch the frame on bumps when loaded with 160 Kg and a full petrol tank. This also was the case with my 4/4 and I changed for adjustable damper. It is not the most elegant way but it helps to keep the rear a bit more under control.
As I am close to the dealer today I might go there for a short stop.
