I have a Tobias (Gibson) Growler 5-string fretless and I've been noticing that the main volume control is getting a bit "crunchy" (annoying static noise when turning the knob through a particular range). Is there some way that I can clean the pot or do I need to replace it? Any other ideas or suggestions? (This seems like Pickups & Electronics 101, but I didn't see anything in the FAQ or Search.) Thanks for your help.