Download Cage (toolbar app)
[For Intel Macs, OSX 10.5 or higher]
Cage mitigates the high-pitched sound defect in Apple MacBooks as described here:
http://discussions.apple.com/thread.jspa?threadID=1004945
http://discussions.apple.com/thread.jspa?messageID=9483474
http://discussions.apple.com/thread.jspa?threadID=1424595
Cage accomplishes this by playing 4:33 seconds of silence on a loop.
Even with Cage running, there may be a low-volume oscillating buzzing sound.
This is regrettable, but preferable to the high-pitched squeaks.
Download SINWAV (noise app)
[For PPC Macs, OSX 10.4 and higher]
SINWAV produces sinusoidal tones with various distortion effects
Download Duck Hunt (mp3 downloader)
[For PCs, Win98 and higher]
Duck Hunt downloads mp3s (or ducks) randomly from the internet. Your catch will be a surprise