I have this subwoofer that I bought new several months ago and I can't make it stop humming. When no RCA cable is hooked to it, it is silent. When an RCA is hooked to it but not to anything else there is a loud hum. Hooking the RCA cable to my receiver reduces the hum but it is still there and it also induces a small hum in the main speakers. My system with all it's components is dead silent at idle until I plug this sub into it. I checked the Klipsch forum and it is a common issue but there are no solutions other than try new cables, check the electrical outlet, etc. No schematic was provided with the unit and I don't know if one is available. I am going to open this baby up and see what I can see. Any input from the Pros at AK is much needed and appreciated.