Audio Systems: Home theater - Onkyo, HDMI cable, parasitic oscillation

Question
Hi, I just purchased and hooked up an Onkyo TX-SR805 receiver to a 7.1 surround sound t.v. room set up. I installed a 7.1 wall plate and have speaker wire running from the receiver to the wall plate and then in the ceiling and walls to all 7 speakers and a coax to the subwoofer. The receiver handles all the HDMI inputs and a single 35 ft. HDMI cable runs out to the Samsung LCD TV. Question, at random times during t.v., DVD, etc. I sometimes receive very loud feedback/static. After this 4 or 5 seconds of feedback, I either have to turn off the receiver or hope that the audio comes back. The feedback sound is not controlled by the volume of the receiver, and is loud at any level. I've checked connections into the receiver and nothing is touching or crossed. Any help is very very appreciated. Could there be interference from electrical lines or anything else in the attic or walls? Or could it just be an issue with the receiver processing the surround sound?

Answer
Not enough descriptive information for me to tell what is going on. If you could record the sound you are getting and send it to me that may help me to identify what process is being activated.

Just guessing it could be an instability that is just on the verge of the unstable point.  These are usually parasitic oscillations of one kind or another.

The 35 foot HDMI cable seems pretty long!

Try dressing wires away from speaker wires.  For example if the HDMI cable or the dvd audio cables are too close the speaker wires you can get electrostatic coupling.  Redress them as far away as possible and see if that helps or solves the problem.

Best to you,
cleggsan#cleggsan.com