I have a Dish Network Model 722 DVR (pictured above) connected to a Vizio E420VO HDTV via HDMI. When I turn the TV's volume up above 0, I get a slight low-level hum, almost like a 60Hz hum, which does not increase as I raise the volume level. If I turn the volume down to 0, there is no hum. The audio from TV programs is loud enough to mask the noise when listening at a normal volume level. I tried another HDMI cable with no change. It doesn't happen with my LG Blu-ray player; I even swapped the inputs, and the noise followed the DVR. The cables are 6-foot HDMI and not expensive. Everything is plugged into an APC uninterruptible power supply unit, though the hum happens with or without the UPS unit in line with the AC outlet.
Am I making a big deal out of nothing? Should I just ignore it or try to cure this low-level hum?