Guitar hum can be very disruptive and annoying, especially if recording. The most common source of guitar hum is the pickups. Pickups are microphonic and therefore prone to radio-frequency interference (Reference 1). The hum will be exacerbated by various external factors, such as poor household wiring and the presence of fluorescent lighting, but there are mitigating steps you can take to minimize the amount of hum your guitar kicks out.
Troubleshoot the guitar. Plug the guitar into the amplifier and turn the volume dial on the guitar up to full. Gradually increase the amp volume to your preferred level. Clasp your hand around the neck of the guitar. If this stops the hum, it is a sign that the pickups are responding to radio-frequency interference. While you can’t stop radio-frequency interference, you can insulate your pickups from its effects. If grasping the guitar doesn’t stop the hum, try the amp in the room. It may be that the circuit is poorly insulated. Strip lighting, fairy lights and dimmer switches can cause guitar amps to hum.
Remove the strings. Use a string winder for speed.
Remove the pickups. Unfasten the two screws either side of the pickup cavity. Gently lift the pickup out of the cavity and lay it to one side. You don’t need to disconnect the pickup wiring. It should be long enough to allow you to move the pickups out of the way.
Cut a piece of self-adhesive copper shielding tape to the approximate dimensions of the pickup cavity. It doesn’t need to be an exact fit. Peel away the adhesive strip. Pull the pickup wires to one side so that they are tight. Line the shielding tape inside the cavity in the same way you’d line a cake tin with waxed paper. Push it down into the corners. It will cover the pickup cavity and pickup wires.
Use a pocket knife to score away the excess shielding tape from around the top of the cavity. Carefully score around the edge of the pickup wires, so that they are free to move.
Place the pickup back in the cavity, on top of the shielding tape. The copper will insulate the coil of the pickup from radio frequencies, which cause hum. Screw the pickups back in place.
Unscrew the back panels to expose the potentiometer cavity and spray a small amount of plastic-safe contact cleaner onto the potentiometers. Turn the volume and tone dials to distribute the cleaning solution around the potentiometer. You should clean your potentiometers as part of your guitar maintenance regimen, but it’s particularly useful to do so if you are trying to reduce unwanted hum. Dirt and grime on the potentiometers can cause unwanted noise, including hums and crackles.