Okay, I have several new data:

1. There was no fluorescent light in my room. The closest CFL is two rooms away.
2. There are no dimmers or "choppers" in the house.
3. My DAW froze briefly yesterday. During that time the static noise disappeared. Does this point to the VPU? (I hope not, I paid $200 for that sucker.)
4. And the biggie: I put in a 3/2-prong adapter, and Lo! both the hum and static have become barely audible. As in, I have to put my ear up to the drivers to hear it. The noise coming from the liquid-cooled PC is louder. The hum and static are barely audible from my normal listening position.

Onward.

"My primary musical instrument is the personal computer."