Audio Systems: Popping Speakers, amplifier section, output amplifier

Question
I have a Sony STR-K7000 home theater system, bought 1 1/2 years ago, that has a popping noise across all 5 speakers (not the subwoofer) about 5 to 10 seconds between pops.  I have a comcast cable box (composite), Sony 5-disc DVD/CD changer (HDMI), and a WII (component) that all hook up to an LG LCD TV 47LB5D.  The only cable going to the receiver from the TV is an optical cable hooked up to the video2 input on the receiver.  I connected the receiver with only the speakers hooked up and the speakers still popped.  I adjusted the volume (just speakers) and the popping stayed at the same level.  I had this receiver hooked up a different way about a year ago.  Everything was hooked up to the receiver first (didn't have a digital audio out on that TV).  If I remember correctly, when the DVD/CD was hooked up to the DVD port (HDMI) on the receiver, the speakers popped.  The cable box was hooked up to the video1 input on the receiver (composite), I don't remember the speakers popping when cable was watched.  Please help me solve this problem.  Do ferrite beads help with popping speakers?

Answer
Th fact that the speakers still pop with nothing else connected shows that the problem is within the receiver.  Basically there is some DC voltage coming through to the output amplifier section.  This unit needs to see a service bench.  There is probably a defective dapacitor in the unit that is causing this.  Does the popping change volume with the volume control?  If not, then the problem is isolated to the output amp section.  Otherwise the problem is in the front end.
Dan