I have a Sony system I pieced together, can't remember the receiver model right now but every once in a blue moon it would produce a loud pop, (you'd think the speakers were gonna blow up) and then it would shut off. The receiver display then said "protect". I could shut the system down and turn it back on and it always came right back on. I've gone through all my connections etc. can't find anything. This morning I turned the system on and in came up in "protect" mode. Nothing I do changes it. Any ideas?