I am in the same boat. Real bad case of EMI and I have shielded all of my guitars with only minor improvement. I built a portable EMI sniffer (battery brick -> high gain 40db solid state amp -> single coil pup, and small speaker) and have mapped out the worst areas of my house. They are all near electrical outlets and wire runs in walls and under the floor. I have an old house and some outlets are not grounded (they only have the old 2 prong sockets). I have not been able to identify any particular appliance that might be causing the noise, but I haven't ruled that out yet . I think I'm going to put my sniffer in a noisy location and have my wife cut power at the fuse box to various rooms and see if I can narrow the search. If I cant find a particular device to turn off that will help quell the noise, I am planning on calling an electrician out and show him my problem to see what he can do.
Oh, and I should add that I've had my Kemper and guitars out of the house and they always sound way better just about anywhere I go. Way less noisy, and then I always come back home and swear at my stupid house when I cant get a good mojo going because of the noise.