Jamie - the motor bearings were very dry and caked with dust - the front bearing was the guilty culprit - a bit of play there but so dry with no lube - you need to remove the side clamps from the motor and seperate the two halves - but the carbon brushes should be removed first or they will spring out when the commutator and armature is pulled out of the rear bearing housing.
The belt does slightly rub in the plastic due to it riding on the end of the motor spindle, but this does not make the noise - the noise was purely bearing oriented.
