I think you mean the bush inside the gearbox that the starter shaft pushes into. This usually only makes a noise when cold if its not in straight or damaged. Maybe difficult to replace yourself if you haven't got anything to prise it out with.
My money is on a problem with the motor itself. The way to check if its the bush is remove the starter, put grease on the end of the shaft, refit, see if the noise disappears, if it does then probably the bush.