Greetings from London. I have had a REL sub for years, and an ongoing problem. The high-level connection cable picks up hum. If I move the cable to in a position that is not in fact convenient (i.e. across the floor), then it's fine. But put the cable where it ought to be, and there is a persistent hum, annoying if the sub volume is raised. The cable is in fact longer than it need be. I've checked the connecting plug at the sub end. Would shortening the cable (which I could do quite a lot) make a difference?