the trick as told by black napkins will only push the dirt/dust away or to another area and its not a fix.
the way to fix pots that crackle it to clean them.
This can be easily done with pot cleaner. make sure you get a kind that wont eat thru plastic.
i use Deoxit only, but thats me.
to do this,
expose the pot- this may require serious tear down/rebuild of the housing depening on what you have but a valvestate just has the top 6 screws; (make sure you dont let the amp crach down when removing the last few screws)
then, on each pot, there is a small opening if you will, spay the cleaner in the pot and THEN work the pot left to right in full rotations for a minute or so. once you've done this once, repeat.
If this doesnt fix the problem,(almost always does if done correctly) then the pot will need to be replaced..
also be sure to check for cold solder joints before replacing the pot as well.