When I connect my receiver (rca output) to my subwoofer amp (xlr input) with an RCA -> XLR cable the speakers produce static and a tone, however there is no static or hum on the subwoofer. The tone is not exactly a hum so I don't think it's ground loop noise, but I am inexperienced and don't really know. The static/tone occurs even with the subwoofer unplugged and the amp is powered off - as long as it is connected to an outlet. The volume of the static does not seem to be effected by the volume on the receiver. I've tried connecting the receiver and amp to the same outlet, different outlets, and both the battery backup and surge protector sides of my UPS. I've moved cables around with no change, so I don't believe it's a noise from induction either. I'd be willing to purchase something like a Furman M-8X AR if I knew it would resolve the noise problem, but since the battery backup didn't change anything I'm hesitant to throw money at a line conditioner. It's probably also worth noting that the Marantz receiver power cable doesn't have a ground.I'll be borrowing a receiver this weekend to rule out my receiver being at fault, but we'll see.