I've found out that the whirring from the back is not the UJs, Diff or the wheel bearings. It seems that my rear propshaft is knackered. To be precise there is one hell of a lot of play where the two parts of the shaft fit together, the splined part.
I always greased it a fair bit, but a while ago I split the two parts and the plastic coating on the male part came off. I thought it would be OK, forgot about it and now it's very knackered.
60 something quid from paddocks, wonder if it comes with new UJs too.....Guy