1. Pots crackle. Bad pots. You could try cleaning them with some Radio Shack tuner cleaner but it would be better to replace them.
2. Could be the cap but more likely either the pot has gone bad (missing carbon on the pad until it hits a good spot) or someone has put the wrong kind of pot (log vs audio or something like that) in it.

Are these humbucker pickups or single/double coil rails?