sounds like the guitar is not shielded in the inside cavities, you can cover all the cavities with some thick alu foil glued in and connect that all with a wire to the ground connection ( the hull of one of the potmeters normally ) or you can buy special shielding paint in a good music store but that will cost you more.

This will help a lot in reducing the noise but you have to be up for it, it's quit some work. See the next video ( don't forget the back cavity )

https://www.youtube.com/watch?v=SH3hEj18uV0

Herman