Here’s a quick test to determine if your potentiometers need to be replaced or just cleaned. With the guitar plugged in, try turning the scratchy pot back and forth quickly a few times. If the scratchiness starts to lessen, then the pot needs cleaning. If the scratchy sound doesn’t go away or sounds more like a “click,” then the pot needs to be replaced.
To clean dirty pots, you’ll need a spray cleaner or lubricant commonly available at any electronics parts store. With the guitar unplugged and the pots exposed, give the pot one shot of spray through the opening in the back of the cover that protects the pot. The access hole is small, but by using the tube supplied with the spray can, the spray will reach inside the pot. One shot should suffice. Let it set for about 10 seconds and hen rotate the pot back and forth quickly. Plug the guitar back in and give it a test. The noise should be gone or reduced significantly. If there is still some scratchiness, unplug the guitar and repeat the process one more time. If the scratchy sound doesn’t go away at this point, it’s probably a bad pot and it’ll need to be replaced. Just a note of caution — before you spray anything in or around your guitar, protect the paint job by putting a towel or old T-shirt around the body.
from Seymour Duncan