What he said... pot wipers are actually made up of multiple fingers so when one or two bounce up off the resistive substrate there is at least one or two still touching to complete the circuit. When the pot is dirty, or badly worn, you can get these audible perturbations as the pot is turned. Some circuits with DC current flowing through the wiper, like old school bipolar opamps, can be a little more sensitive to wiper bounce.
Sealed pots should never get dirty. I have never heard from a pot manufacturer that ever endorsed a pot cleaner/lube while they may have an interest in selling more pots. Even in one obscure incident with Alps, who was one of the better pot makers I worked with, they were pretty tight lipped even about lubricant advice. The obscure problem was some static effect compounded (or mitigated) by the lubricant, so apparently lubricant isn't even that simple.. it needs to conduct enough to drain off static charge but insulate enough to not affect the resistance.. Of course this (static) depends on materials used and more but this all has nothing to do with your question.
No magical fix, while a bad opamp or circuit that puts DC on the pot could make it sound dirty (scratchy) when it isn't. Real dirt under wipers often abrade the substrate, so rather than self-cleaning, its more like self-destroying, and a candidate for replacement.
JR