Ksa 300s

I had a KSA200s & it was dead quiet.  I could turn the volume quite high with nothing playing & it was like it was not even on.  I was using a Krell pre amp as well if that matters.  
On a sad note the KSA did fry itself after a while and I replaced with a FPB300cx which is just as quiet.  
Perhaps this will help.
-John

Are you using rca or balanced cables?  If rca, you need to connect a jumper pin between pins 1 and 3 of input balanced connector on amp.  The negative input must be shorted otherwise you will have noise issue.

sfstereo:  That is an extremely good point that I had completely forgot about.  FWIW - I was using balanced.