welcome aboard, its a pretty quiet list.
given the stats you posted the noise is pretty faint,
an annoyance no doubt but pretty low. if you're recording a guitar, and you compress
(or actually i just suggest 'remove silence' once the tracks are in the PC) it i can't
see how it will actually affect the real quality of the track when you are done. but
you'll probably not be happy with that.
I run my PC into a Back-Ups unit, and perhaps that removes the noise between the two,
since it has never been a problem for me.
does the noise go away when the monitor is turned off?
if you run an extension to a totally different outlet does the noise go away?
test it a little more and that will give more info to go off of, then maybe we can
narrow it down.