Hi, CJ! Welcome to TheFret. Stop by The Players forum and introduce yourself!
Keep in mind that the P90 is a single pole pickup design, and therefore very prone to AC hum. If you switch to the dual pickup position, I would espect that to be hum cancelling and most of the noise should go away. It's not likely that the pots have much to do with it--cheap unshielded wiring and lack of good shielding & grounding practices in general are probably to blame. There are many excellent ideas for things you can do HERE.