FWIW, a bit of an update on this
Last week I was moving to W7, so I placed the CPU into the center of the room, for accessing the hard drives and whatnot. Patiently, I tried to identify the source of the hum, until finally found out it was coming from one of the fans mounted in the case (before, I was convinced it was either the power supply to blame, or the processor's fan).
So, grabbed a screwdriver, and simply started to loosen and tighten the screws, until I got the noise-vibration reduced as best I could.
Today I went about the
daunting task of clearing the closet
wash the walls and vacuum the carpet floor inside it. Cleared the space and placed the case there, damped it by placing some large pillow on the side (leaving proper space for air to flow on the back of the case), placed back some clothes from hangers, and closed the doors..
The result is simply AMAZING! I know it probably sounds somewhat unimportant, but now I
literally cannot hear any noise whatsoever!
That low, constant,
constant humming frequency was
really driving me nuts, and also really getting it the way of things for me
So, happy day, and $0 spent
EDIT: I did end up getting extension cables couple months ago for the monitor, the power cable, and a hub for all the USB stuff (I will still need longer individual cables for those, specially for the rack POD).
Thanks for the advice Steve!