Found out what was causing a knocking noise from the rear of the GV!
Bushes on both rear shocks completely shot. As far as I can tell the self leveling shocks are still ok. (New ones are pretty damm expensive)

Running with standard shocks now until I get round to fitting new bushes in.

 

If there's anything that I like its pictures, tells a better answer.
Here your drives like mine, Mono-Blocks. Nice but grows weed/moss especially where not in the sun...
Goggs.

 

New bushes installed. Quiet as a mouse now!