Hi, I've noticed what cause this high-pitched sound I hear when I use my iMac G3 (slot-loading). I couldn't identify the problem first. It's the monitor that causes this... I installed SwitchResX for changing the resolution first - The G3 monitor seem to support a maximum of 1024x768. I plugged it to an external monitor (Which support a maximum of 1280x1024), and SwitchRedX allowed to use 1280x1024 with the external monitor. Choosing this resolution will work with the external screen, and cause the iMac screen to turn Off. And the high-pitched sound is gone! It's not related to the OS, because it does it during the Apple logo, and on Linux as well, when the monitor is ON. It's weird... Definitely hardware related, but I can't tell what's wrong (Not worth it to fix it for me, I'm curious about it). Thanks!