I received a brand new BK XXLS 400 sub the other week, it works fine, BUT I was experimenting the other day, and noticed a "HUM" that got louder, as I turned the gain up. I have been told its a mains hum (earth?). So i moved it to the back of the room, behind the sofa, and its plugged in to its own socket, and connected by a 10 meter sub cable, that I just bought via Amazon.... It made no difference at all, the "hum" was still there. Is there any way of getting rid of it, changing the mains lead to a non earth type, as its earthed by means of a connecting cable to an Anthem sub out?