I did not see a direct answer to this question - if there is one please send me in the right direction. I recently installed a home theater system with projector. I have an Onkyo TX-674 AVR and run the dvd and projector through this receier using HDMI cables. Initially, I only played dvd's and did not experience any hum. When I added my comcast box, using component cables, there was a new and loud hum - primarily from the sub woofer but which can also be heard from all speakers. I have replaced the cables several times with no significant change. I also installed a radio shack ground loop isolator to no avail. One connection from the component cable is enough to cause the hum.