More details about the guitar? Is it a 250k or 500k pot? What are the settings on the amp?
Why dont you start by opening it up and looking to see if there are any loose connections, wires off, bad/cracked solder points, etc....

If everything is well, i would just replace that particular pot. Its like 3 bucks, and easy to change.
Jackson SL3 Soloist
89' Ibanez RG570
Vader 4x12 Cabinet
Line 6 HD147 Head
6space HEAD/RACK case
Korg DTR1000 Rack Tuner
Furman Power Conditioner
ISP Decimator