Alex i know you said your getting coilovers soon but maybe you can get someones old rear dampner (from someone who got coilovers fitted) then you can see if its that with out the expensive of new units (dont wnat to reaplace it if its not at fault)
 
I have a similar problem to this thread.

Grinding/groanin coming from the drivers wheel on turning left, this started before fitting my ycoilovers and is gettin gradually worse now especially at 40mph.
 
Scotty_b said:
Alex i know you said your getting coilovers soon but maybe you can get someones old rear dampner (from someone who got coilovers fitted) then you can see if its that with out the expensive of new units (dont wnat to reaplace it if its not at fault)

It was tyre noise as once they were 'worn in' it stopped! I sometimes get a funny noise on some roads which i put down to it being that too