I am having the same issue. I hear a constant hissing as soon as the speakers are powered on. I believe it may be coming from the 9-pin pre-amp input but it is constant. The only thing that stops it is turning it off. I also tried different outlets and even one from another room with an extension cord. I upgraded from a very old Boston Acoustics 2.1 computer speakers an never had this problem. Is there a resolution or a known fix?