Need some advice. Just hooked up an Onkyo HT-S590 system. When I switch to any Surround Mode- (PLII), I get a hiss from all five speakers. The hiss volume is not correlated to the amp volume. It stays no matter what the volume is at, muted, etc. Is this something I can fix, or do I have defective equipment? Will an Optical hookup solve the issue? (I'm currently using digital Coax).