Mine's not scratchy but, for the sake of this thread, I took a look and the pot and mine is sealed with no place to spray lubricants in the back. If yous is like mine, I'd recommend unracking it and holding it with the faceplate looking up. Remove the big knob (will probably need an allen wrench.), and spratying a little pot cleaner at the base of the pot's shaft and turn it wildly in hopes that some of the cleaner will make its way inside. This sometimes works, sometimes doesn't.
This stuff makes a mess so mask off the rest of the unit.