I do this with every guitar I buy and decide to keep:
Electro-static Guitar Graphite Shielding paint and a ground wire.
I got a kit, but you can get any kind of shielding paint. I got a 2oz bottle from a seller on reverb. I painted four guitars and have plenty of pain for another guitar or two.
This is what I do. I start by removing the electronics and pickups. Then I paint interior of control cavity and pickup routes. I make sure I get the sides and as much of the wiring routes as I can. Be sure to cover your guitar's finish if you're not good at detail painting. The graphite in the paint will dry in a silvery-like finish that doesn't rub out of the finish on your guitar, so don't make a mess.
I usually put on two coats.
I get a few inches of 20-22g wire and a small wood screw. I screw the screw into the cavity somewhere out of the way, and attach one end of wire to the screw. I paint the screw with the graphite paint.
Next, I reinstall all the electronics in the manner I want. This is usually when I change out the pots or pickups, etc. Once everything is installed and all set, I then ground the other end of the wire to a pot or other ground in the electronics cavity.
I button the control cavity up and give it a run. At my house, I have this annoying overhead LED lighting system in the kitchen. If those lights are on, no matter what, I get hum in my studio that I can hear, and it's super annoying. Once I paint my guitars control cavities and pickup routes with the graphite paint and ground it, I get absolute silence. No hum, no static, nothing. It works awesome.
Before I used this paint, I was chasing this hum all over the place. Got new cables, RF filters, got an expensive clean-power double inverter, etc. Nothing worked. Except $10 worth of conductive paint and an hour of my time.
I have never used this paint with a PCB setup, but I don't see why it wouldn't work the same way.
Good luck!
