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.