Thanks. There is no hum at all coming from the other speakers with the receiver off. The only hum is coming from the sub, and, like I said, it goes away with the phase moved to 180. Someone mentioned switching the RCA cables around but I only have the single RCA sub cable coming from the receiver, it's not a red/black cable. I'll do some cable jiggling later on to see if I can get it to go away. If it does, it's either the cable connector, the sub connector, or a faulty/dying board. I've been trying to contact the mfr, Emotiva, but have been unsuccessful so far.