you could try getting a can of shielding paint from stew mac. apply at least 3 coats everywhere inside the guitar cavity. I find that a foam brush works far easier then a bristle brush. then run a metal screw inside the cavity and connect a wire to it and then solder that to your guitar ground. make sure you drill a pilot hole first and make sure you wont be drilling through anything so the screw sticks outside the cavity.
Yikes!!
This does really help. (the shielding paint part, not the drilling through your guitar part, lol)
But first obviously you want to check all your wires, pedals, and outlets you are plugged into. could even be a fuse starting to go bad inside your amp. I live in an old house (1753!!!) with old wiring and I've had problems with all of the above from time to time. make sure the outlet you are using is properly grounded, etc. even if I have too many lights on in the house that can be an issue once in a while.
After that, my guess would be waxing the pickups maybe, but I think hallmark already wax them, but I could be wrong.
I also use a "Hum-X" adapter I hook to my pedal board to reduce noise. since I bought it, I've had far fewer issues with hum on that end.
hope this helps.
