As I've detailed elsewhere, I had persistent hum from my twin Velodyne subs. I suspected the Shaw Cable installation after much reading on the net. What was interesting is that a 'Customer Review' at Future Shop slammed this model (DLS-3750) for having a loud hum & he returned 2 of them to FS. It most likely wasn't the sub's fault at all.
After many unsuccessful experiments over considerable time, the only method that completely killed my hum was to attach a jumper wire from the outside barrel of one of the unused subs' RCA Jacks to the outside barrel of an unused RCA Jack on my Sony XBR TV. Alligator clips work great for this or you can build a harness using only the outside connection on the RCA Plug.
Interestingly, attaching the jumper to the Cable TV Coax outer shield did not work.