dual sub set up, one hums but not the other?

[blue11]

I currently have a dual sub set up and am experiencing what seems like an intermittent ground loop issue on one of the subwoofers. It "hums" on and off intermittently, mostly when I change channels. it would hum for a second or two and then go away. When a signal goes to the sub it hums for a bit then goes away similar to the length of time when changing channels, but sometimes it persists for a few more seconds
I don't believe it would be caused by the STB feed since only one of them hums. Would that be correct?

I've tried switching outlets on the power bar I have my components plugged into but the problem is still there. I haven't done a lot of cable management but have tried my best to separate the cub cable from any other cables. I've also tried using the other sub cabe to see if it was a shielding issue but the problem persists.
I've read a few other threads and the gound loop issue thread but I would have to say, I am lost at that one.
Any other thoughts?
Here's a list of my components:

42" LG Plasma
Yamaha RX-V663
Paradigm Cinema 110 CT
Paradigm DSP-3100
PS3 (80 gig)
Motorolla DSR 505 (STB)
Kensington i-pod dock

all but the TV is plugged into a power bar, not an expensive one.

any help would be greatly appreciated.
thanks in advance guys