My mobo also squeals, piggy-like
Actually, it's a faint sound, but it's nature makes it clearly audible and awfully annoying; just like in your case, it's the VRM; I've been able to pinpoint the source by playing with energy saving options.
I only have to disable C3/C6 and the noise is gone
All other pwr saving options are enabled. In real life, as measured by a simple kill-a-watt thingy, this translates to 1-2 watts more consumed in idle. Not a big deal, I'd say, as my PC draws 65W in idle and around 70W when I work (text editing, etc.)
In the past, my 775 board would also produce such a sound, but only if certain overclock was configured. After messing a little with voltages and clocks, the noise was simply gone.