Does the sub hum when it's signal cable is unplugged? That low level hum may be that the signal and power cable are too close. Try separating them and see if that cures the problem.

Try unplugging one component at a time from your UPS and see if the problem clears or try plugging all of your equipment into a single power strip (just for testing). Does your UPS include your phone and internet connections? If so you may need a filter on those. They are generally buried outside and have their own grounding system separate from the one in your house.