A couple of years back, I learned that I have a superpower. Turns out this little oddity is common among people with ADD, though as far as I know I do not have that disorder. What was actually surprising to me was not that I had this power, but that most people did not.
I can hear (or perhaps "hear") a cathode ray tube in operation. There is a very quiet high pitched whine made by monitors and televisions in operation. Most of the time I am unaware of it. But whenever a computer is turned off I can hear the monitor until it is turned off, whenever a monitor is turned off it makes quite a bit of noise, and if I wake up in the middle of the night and a television is going in another room I am almost always well aware of it even if it is completely silent (playing a DVD player main screen, for example) and before I am in a positio to see light from it.
I've known this for a while. Somewhere I have some links to a slashdot discussion on the phenomenon.
But just now I made quite a discovery. My previous monitor at work responded strangely when the general color composition of the screen changed: switching from a screen that was mostly white (text document on a black background) to a screen that was mostly dark (selecting all the text on that page) would actually resize the visible image. Really weird.
That monitor went nuts a couple of months ago and I appropriated the monitor of a departing colleague. So today I'm working late in a very quiet office and as I was selecting and deselecting a couple of paragraphs, I noted a cricket chirping. Then it fell strangely silent. A minute later I performed a selection, and the cricket chirped again. I alternated between ctrl-A and clicking my mouse to select and deselect, and realized that the "cricket chirp" is my monitor. This one doesn't resize anything when the color composition changes, but apparently the monitor sound gets louder and/or changes pitch.