Hm. I got an idea that MAY be right. What is clear to me, that there"s a strong noise source. This can affect my pick-ups, or the electrics inside the guitar.
The electric can be shielded as you have described earlier, but I think I could try to bind the strings together electrically, and binding them to the common earth of the pickups (or maybe just binding them together).
I don't know if I'm correct but this may work as a screening conductor, and so may decrease the noise recieved by the pickups.

Is this possible?