Quote Originally Posted by Triathlete
Did you try reversing the polarity?
That's the first thing that came to mind with me too. The easiest way to ensure correct speaker-wire-terminal/speaker-wire polarity is to put a 9-volt battery (the small square ones) across the speaker leads. When applying the battery across the leads makes the speakers' woofer push outward, the positive battery terminal is on the positive speaker terminal. Check all the speakers just to be sure.