Wolf-garten 6.40ea Self Propelled Mains Electric Lawnmower

From a recent dealer clearance we have this 16in self propelled mower from top German maker Wolf-Garten.All looks in good order visually, and appears complete except for the grassbox.It does run and the drive works okay, but there is a physical grinding noise coming from the base of the motor as though two bits of metal are contacting occasionally - I have had a quick look but cannot see anything obvious. For that reason, although it is working , we are selling it as spares or repairs .Expensive, top quality, machine.