I'm aware that fan noise and power supply issues are fairly common on the iMac G5. My Rev A model, however, has been problem-free... until now. Recently I've noticed a high-pitched whine of sorts emitting from the top-center or -right of the computer. The sound was definitely not there before. I find it hard to characterize the whine with great specificity; it almost sounds like a loud electronic hiss. If you're at all familiar with the infamous MacBook idle processor whine, you'll have a good idea, only this sound is louder than that. Also, the computer will no longer stay asleep; resetting the SMU and the PRAM did not help. I should note also that, 1. The computer passes the Apple Hardware Test. 2. The whine disappears when the computer is asleep or off. 3. When the computer and display are awake, it is constant in pitch. Processor-intensive tasks do NOT make the whine louder. 4. The pitch of the whine changes in the seconds immediately before the computer sleeps and after it wakes. 5. During the start-up sequences, the display dims and brightens. This is particularly noticeable on the white screen with the gray Apple logo. I would suspect the power supply, BUT.... 6. Lowering the brightness of the screen does not reduce volume of the whine. Can anyone hazard a guess as to what problem my iMac may have? I hope it's nothing too expensive, especially if it renders my computer a ticking time bomb.... In any case, I appreciate any help you all might offer!