I worked out what was making the high-pitched whining noise in my office - it was the old XP computer (the one that iTunes now refuses to run on, after running just fine for a year). I've got all the functions it was doing, onto a Windows 7 box that I bought so that I could run Civilisation, and the new box is nearly silent.
So the next loudest thing was my big UPS; it has a fan that is relatively loud. So I replaced that with a UPS that runs silently.
So now, the only sounds I can hear are a very quiet fan in the Win 7 box, the occasional car trundling down our little country lane, and the thing upstairs that we call "The Roarer" which is something to do with our heating system, but I never found out what. And, of course, the sound of typing on my big clicky IBM keyboard. And occasionally, someone using the Geocaching Robotic Arm.
The sound of silence.