Ever since 10.2.4, I got a high pitch soft whistle too often with my 15" TiBook. Mail.app, if open when I put the computer to sleep, always freezes after waking -- with that high whistle humming in the background. Clicks or keystrokes *halt* the whistle, or interrupt it for a flicker -- but then it's back on again, as soon as you release.

Force Quitting Mail stops the noise. I had heard the noise before -- notably with Help as of 10.2.0, but this is the most consistent it's been. Other apps function fine when Mail is crashed and whistling.