I hope someone can help me with this problem. Sometimes as I`m viewing a movie, i am not experiencing sound from my left surround sound speaker and my sub-woofer. I have in the past shut the power off the receiver and then turn it back on. The surround system then works fine. This has happened to me several times. I have a Yamaha 5.1 AV receiver. I find this very frustrating,and do not know what causes it. Please help.