I have an Acoustic Research prepowered subwoofer that hums. It doesn't hum when the RCA cables are unplugged from the back of the Sub. The setup consists of a high quality Y coming out of the pre amp output of the receiver to a high quality 10' RCA cable that connects to the L and R inputs on the sub. Also, when I plug up only the left or only the right, the humming will start, but if I touch the pole of the other cable to the outside metal jacket of one of the other connections on the back of the sub, the humming will stop. Could the cable be bad? Am I hooking this up incorrectly or are you supposed to split the signal from the back of the receiver? BTW, I just got a new receiver and the problem existed on my old receiver as well.