NEVER use WD-40 to clean a pot. It doesn't conduct too well? Well, think about it - wouldn't any conductive cleaner short-circuit the pot??
Pots get scratchy primarily because of dirt and dust, and through oxidation that may have built up over time. The rotating slider moving over enough of it sometimes make good contact, and sometimes does not. This make and break of contact is what causes the crackling noise.
Get a decent tuner/control cleaner. It will dissolve any oxidation and blow away any dirt and dust. A decent cleaner will also have a slight lubricant, usually a mineral oil, that will help lubricate the moving parts.
Make sure you check out the controls - for example, the Drive control on the Beta is a dual pot, so remember to spray both sections.
When spraying a pot, do not overspray and try to get what you do spray inside the pot and not all over the circuit board - clean up any excess with a paper towel if you do overspray. Use the spray tube that comes with for better accuracy. Protect your eyes. Rotate the control multiple times after spraying. Wait for the cleaner to dry before plugging in or powering up the equipment - normally about 5 minutes. You did power off and unplug before you started... right?
