Background Hissing Noise When Idle

I have noticed a very slight background hissing noise coming out of the speakers when my system is turned on but idle - that is, when I am changing cds and the preamp and amp are turned on. This hissing noise increases as the volume increases, and can be heard as a slight background noise even when the music is playing.

What causes this hissing noise? Is it coming from the amp, the speakers, the preamp, the electricity itself, etc.? I know this is not a big deal. Then again, in our quest to become true audiophiles, I suppose any level of background hissing noise will distort the true sound quality.
I currently have a Krell KAV-1500 amp connected straight to the AC outlet on the wall. My Lexicon MC-1 preamp and Krell KAV-250cd player are connected to PS Audio Power Plant 300. I also use Cardas Golden Reference and Shunyata Black Mumba power cords. My speakers are B&W Nautilus 801s.

I thought that with my setup, I should hear no background noise distortion. So, is there any way to eliminate the background noise completely, or is this something I have to live with, as there is really no holy grail solution to this problem.

Your thoughts and experience would be greatly appreciated. Thank you.
It is possible that it could be noise from the circuit that the power amplifier is plugged into. Is this dedicated circuit? If not, that's where I'd start.

If it is a dedicated circuit, then I'd borrow a power conditioner from a local dealer and see if that solves the problem. In order to preserve the incredible dynamic range that your system can reproduce, make sure you try a filter that can deliver all the current your amplifier needs.
Chang makes a unit specifically for power amplifiers. That's what I'd try...
The fact that the hissing noise increases as volume increases would indicate that whichever piece is controlling the volume or the source is the cause of the noise. I doubt that it's the Krell gear, so the most likely culprit is the Lexicon processor. You could try reversing its AC plug and see if that helps. Also, unplug the Krell CD player for about a minute and then power it back up. You might also want to buy a cheap AC outlet checker to make certain that your AC outlets are properly configured and grounded. If none of that works, then the only way to get rid of the hiss may be to buy a better quality digital processor.
It's probaly your preamp.
Just a further thought.Go to the PS Audio website and print the procedure for tracing a hum.It should work the same for a hiss.Basically you need to disconnect everything except the speakers.If there is no hiss from the power amp alone,re-connect the preamp and listen again.If still quiet,re-connect components one at a time until the source of the noise is pinpointed.If the noise is from your ac line,a parallel filter might help.Good Luck!
I agree with Gthrish1. I would look into AC noise coming
into your system from your AC outlet. I just moved up to
a McIntosh setup that required more AC outlets than I had
used with my prior system.
When I first set up the system, I was using two lower
cost power strips. My system sounded overly bright and
there was a slight hiss in the sound - regardless of which
source I used. After a week or so, I plugged my entire
system into a Panamax 5300 Line Conditioner - and it cured
all my problems with system noise and brightness. My CD
and tuner music now come out of an absolutely silent back-
ground. Check this item out - Audio Advisor has them for
$499.00 - but I bet you could do better elsewhere.