I recently added a 2nd sub to my HT and notice whenever the Receiver power is OFF the new sub has a constant low 'hum' sound coming from it even when it goes into standby mode (power led turns red) ,but soon as I turn the receiver back on it goes away , should I try using thicker RCA cable? the RCA's I'm using on both subs are pretty thin but they're brand new. I wasn't sure how to split the sub output from my receiver (single LFE output) I used this adapter: Link (http://ded.zenblue.net/rca_adapter.jpg) , Any ideas appreciated.

If you unplug the RCA from the receiver or sub and the hum stops, you have a ground loop.

Thanks I was looking through various 'hum faqs' and long story short it turned out to be bad or unshielded cable ..the RCA's I was using were labeled as "Speaker cable" (extremely thin wires) and one of them was a bit longer than it needed to be (20 foot) I drove to the corner and bought shorter standard RCA cables and the hum is gone :)

Great, I am glad you got it figured out, easily too.