Ok, I have a recently purchased 58 TDV8 and which has the usual front suspension clonks, so it will return to the dealer soon.
However, today, in a long queue for the Nantwich Show... at 10mph the rear of the car started making another odd knocking noise, which was only obvious at low speeds. I nearly pulled over at one stage, but at higher speeds it disappeared. Now, previously I have had a D3 and I used to put it sporadically in offroad height as after a while the ride height would reduce slightly even after a new compressor was fitted. So, after I arrived after 3 years waiting in a queue I pumped up the suspension to off road height and back again, so it is now riding at a inch or so higher than before. And the noise has gone. So, maybe I have a compressor issue...or maybe not...but I think the ride height does diminish after a period of time and maybe the air gets knocked out a little. I dunno...but every now and again I'd stick it on off road mode to put some air in..
Well, that's my theory!