I have a small device I made for the studio for noisy guitars, it's a thin cable with a small clip on one end and a small flat steel plate (about 1" x 2") on the other.
If the guitar makes a noise when the player takes their hands off the strings, I clip the cable to the bridge and slip the steel plate between the guitarists pants and waist so it's touching skin. The guitar player is then earthed to the guitar even when their hands are not on the strings.
I am not talking about mains earth I am talking about grounding the RF using the players body. It only works if the noise stops when the player touches the strings. If clipping the cable to the bridge does not work, it means there is an earth problem within the guitar itself.
Cheers
Alan.