1) Get a multimeter, digital from Radio Shack is inexpensive (DMM)
2) Measure the level of ground leakage, by connecting the DMM from tonearm betal to the ground on your wall socket. Repeat this for the Naim, tuner etc. Try to do them in isolation (disconnect interconnects).
3) One suspect is the ground loop from your tuner. Have you tried to remove the tuner totally from your equation ? The roof antenna, if professional installed, probably have a ground to prevent lightning, and you added another ground, plus you have audio dedicated ground, and regular househole circuit ground.
Anyway, by using (2), you should find the component that has highest ground leakage, this is the culprit.
(4) While you're at it, make sure that all your audio equipments plug into outlets with same ground. Verify by measuring the voltage between each outlet where you plug in your audio equipment. It may be a chance that one of the ground outlet (in wall) has a loose connection on the ground. If you can fabricate a real ground plug by cutting off the other 2 prongs for measurement, you should then use the 'measurement plug', and shake vigorously in your outlets during measurement to make sure the connection is not loose, which will definitely cause problem.
5) Measure the quality of your AC. Set DMM to AC, measure the voltage difference between your 'neutral' and 'ground', and measure between your 'hot' and 'neutral'. The value between 'neutral' and 'ground' ideally should be low, but if you have AC quality issue, you get a high voltage reading here.
Give us the above info, and we continue.....
(*BTW, I really wanted to help, but I just could not send e-mail to you, if you can setup an Yahoo mail or something, then reply back to me).