I hooked up a sub yesterday. Nice little energy e xl-s8. I am happy with the sound but annoyed at the hum it makes when I shut off my receiver, a Cambridge Topaz SR10. I have owned the Topaz since new and it has given me no problems. If I shut the Receiver off, the hum starts. I thought it might be the sub so I gave it some time as I understand the sub should shut off after a bit if time with no signal. I gave it an hour and still a hum. I decided to unplug the Cambridge and the hum stopped. So even with the receiver off, it seems like there is still some signal going through the sub out?? When the receiver is on and playing, even at very low volume I can hear no hum, it is only when the receiver is plugged in and off that it is there. Any suggestions? Or is this just an issues with receiver design. Maybe just plug them both into a power bar.