squealing/grinding reverse only?

I fitted a new clutch kit and after around 30 miles with no problems I have now noticed a squealing/grinding noise in reverse only.
It sounds like metal on metal I have been told its my release bearing but since it is new and seemed to have no defects when I checked before fitting I don't think it is.  It happens when moving off in reverse only when slowly engaging the clutch.

Thanks in advance for any advice