I have just added a Comcast cable box to my home theater setup. I needed to run an RG6 cable from my junction box to the cable box. I used a 25 ft. Quad shielded RG6 cable from Radio Shack. Whenever I turn on the lights in the theater I get an annoying hum from all of the speakers. If I unplug the coax cable from the cable box or if I turn off the lights the hum goes away. The cable junction box is in the next room and even if I put the cable box in that room and run the HDMI cable through the wall to my Onkyo receiver I still get the hum. The lights are controlled my a Lutron Maestro IR Dimmer and are 4 150 watt halogen lights.

Is there any way to get rid of the hum?

1st... have Comcast come and check that the incoming cable line is grounded properly.

Sounds like a grounding problem, also check the tightness of your connections.

You guys where right, it was a grounding problem. I didn't have Comcast come out though, I hooked up a ground myself.