I just got a Dunlop (EDIT: oops, not a Morley) bass wah from eBay today, so I plug it in and I get some crackle when rocking back in forth. It always happens in the same particular place. Is the fix as simple as buying some of that pot cleaner spray stuff and spraying it on there? If so, where do I spray it exactly? I took the back off the pedal and I have a great view of the pot itself.