I have a Denon AVR-788 which is powering a pair of Polk Audio Monitor 5jr speakers (front) and Pioneer center channel speaker (center), and a pair of Polk Audio in-wall speakers (rear). I've got optical audio lines carrying the signals from a Sony Blu-Ray player and from a Hitachi LED TV into the optical in slots on the Denon. My iPod dock is connected to the Aux through a standard analog connection. Basically, I am getting very strange popping and screeching through my speakers through every input connected to the Denon. The problem is intermittent. Sometimes it starts after listening for a while and sometimes it starts immediately on powering up the Denon. I had originally noticed this problem when running audio through the HDMI inputs on the Denon and it seemed to go away when using the optical cables instead, but has reappeared. Any thoughts? I am fearful that I need a new A/V Receiver, but would love to try any other ideas that anyone might have before moving on. Thanks in advance.