Sorry first time i logged on today
Erm well if it happens, i would just open up the cavity, clean it out. Dust is very annoying and loves living in guitars. Try spraying some CRC (the blue can only, you can CRC in other coloured cans, but they serve different purposes), or WD40 (doesn't last as long though).
It could be a shielding problem, ensure that the leads soldered onto the pots are all ok, if they look dull, whip out the soldering iron and resolder them, keeps it fresh.
If it still does it, try replacing the pot or depends on how much a electronics head you are, i would maybe place a capacitor (non polarised) of a high value, say 10 pF, across the two outer legs of the pot and see what happens, i would just experiment with different values, and see if it filters out the hum.
But eh thats just me.
Merls
