Hissing and Hum through speakers

Hi everyone,
I have a fair amount of hissing and small hum coming through my speakers...when music is played at mid to high volumes the hissing and distortion is very audible through the tweeters/speakers. I don't think it is distortion (not sure how I can tell) I think it is that noise that exists in the system and it gets exaggerated at higher volumes...

I have a Panamax unit where everything is plugged in and the Panamax and amplifier plug in to the same wall outlet.

The noise goes away when I mute my pre-amp (Meridian 561.) But with the pre-amp on and non-muted and any source selected the noise is present. Even when the source is in pause.

Also, I have unplugged the inputs from the pre to the amp (line level) and the noise is still present. Same for my center channel amp, and I also have a third amp with same results..

Does this indicate that the noise is coming from my AC line? I have done most of the troubleshooting (different cables, plugging and unplugging sources, et cetera) that I know and have not been able to resolve...