Thanks. Its a strange one, I drove 30 miles yesterday and 30 miles back and the balance was almost perfect.

I know that the wobbling can vary depending on the position of the wheels relative to one-another (ie long sweeping bends on a motorway/highway will make it better/worse), but it seemed almost perfect last night.

The back end doesn't change much, a constant thrum-thrum-thrum noise - but not an obvious thrumming, its almost as though the tyres have a blister but I know they're all fine. I'm pretty certain its not wheel bearings as I can't see bearings making the back end vibrate to any degree.

Weather permitting I'll inspect the transmission mount and the propshaft mounts tomorrow, to see if anything is amiss.