If you have a hollow body guitar or hollow cigar box guitar, you can have unwanted noise from many reasons. Electrical wiring in your home can be an issue, fluorescent lighting, fans, window unit AC's, dimmer switches, computers/laptops, walwarts, bad cords and some amp issues.
Shielding the inside cavities can help with these issues and often times eliminate these issues. There are a few ways to shield against these issues.
1. Wiring. When wiring your guitar it's best to use coaxial wires because it contains a hot/signal wire that is wrapped by a ground wire inside the outer coating. If your using individual wires for hot and ground, twist the ground wires around the hot wires so that the hot wire will be shielded. Do this with the pickup wires, wires between pots, switches and jacks.
2. Cavity Shielding. You can line the cavities with shielding paint or with shielding tape. The tape is often copper tape, but you can also use aluminum tape. Whatever material is used must also have a ground wire to be fully functional. The tape is over lapped making a continual circuit and then touches the grounded bridge or a ground wire is used to link the tape/paint to the bridge.
Another noise issue is 60 cycle hum from single coil magnetic pickups. This noise can be irritating and most people avoid it by using humbucking double coil pickups or specialty noiseless single coil pickups that are costly.
I have found a way to shield the guitar from noise issues and get rid of 60 cycle hum. Aluminum shielding tape. You go to the hardware store and buy a roll of Aluminum HVAC tape. It's thicker than usual cavity tape and that's what you want. Cover the cavities(top to bottom) and the back sides of any pickguards and provide a ground wire to the bridge. This takes care of all noise and will severely limit 60 cycle hum if not completely get rid of it. One roll of tape will do 1 to 3 guitars and only cost's about $3.50 to $4.00 USD.
I stumbled upon this by making a Reso guitar with a aluminum skillet, 1 Piezo and 2 large single coil pickups. Those single coil pickups were extremely microphonic before and now they were noise free. No RF noise, no feedback and no 60 cycle hum. I couldn't figure out why til I came across a write up by a famous guitar tech and pickup maker: Bill Lawrence. He talked about this weird thing about aluminum and 60 cycle hum.
So, when your in need of cavity shielding and your using single coil pickups, use a large amount of aluminum tape. You'll be glad you did.
The copper tape is good, but the aluminum tape does the same thing and it blocks the 60 cycle hum while being cheaper to buy. Winner Winner Chicken Dinner!
Do have to be careful about those accidental shorts with the shielding tape though.