iMac G5 (#8): Loud humming/buzzing noises: High CPU usage a culprit? How Apple support is handling the situation

We continue to cover an issue with newly shipping iMac G5s where a humming, buzzing or clicking noise (quite loud in some instances) is emitted from the included power supply. In most cases, the noise level varies with screen brightness.

Although Apple's documentation regarding the issue states that only power supplies connected to 220 volt power outlets are affected, we've received several reports to the contrary.

MacFixIt reader Brad Ebel writes "We just connected our 20" G5 iMac yesterday, and today we're noticing a hum. Like the folks who've noticed that it correlates with screen brightness, we have noted that,too. However, in our case we can't bring the noise to silent when we select minimum brightness. We use a 120-volt power outlet."

In a document entitled, Performance Testing of Computer and Video Monitors Samuel Goldwasser offers some more detail on the link between problematic power supplies and unwanted noises. Some of the information is CRT-specific, but the switching power supply section is applicable.

"Ideally, a monitor is seen and not heard. However, there are a variety of components inside that can vibrate and this may be quite annoying in a quiet room or late at night. A buzz may originate from the switching power supply or vertical deflection components. A high pitched whine, squeal, or twittering may originate from the switching power supply, flyback (LOPT) transformer, or horizontal deflection components. Some people aren't bothered by these sounds at all or cannot hear them. Others will be driven stark raving bonkers.

"Listen carefully through the grille in the cover for any indication - even momentary - of annoying sounds. Try all scan rates - very often various resonances will only occur at particular horizontal or vertical scan frequencies. Even with high quality monitors, these problems sometimes occur erratically and no quick test will identify such faults. Obviously, doing this in a quiet location is best."

High CPU usage a culprit? A poster to Apple's Discussion boards, Laurie Gallagher, found that high CPU usage was the culprit behind a high-pitched whine coming from her iMac G5. Quitting a high-usage process using the Activity Monitor (located in Applications/Utilities/) resolved the issue temporarily:

"I've had that nasty whine some of the time and only on some volumes. Whenever I heard the whine, Activity Monitor told me I was using 100% of the CPU. It turned out that the Dock was using as much as 91% of the processor. Quitting and restarting the Dock killed off the whine and it's share of the CPU went back to 0%. Your mileage may vary, but on every whiny volume I found the same problem and the same procedure worked."

How Apple technical support is handling the situation We've obtained an actual transcript (edited for length) detailing how Apple is handling the power supply noise issue on a case-by-case basis -- instructing customers to log in to the iMac G5 Troubleshooting Assistant site, enter specific information, and self-obtain and self-install a new power supply:

• Agent: Thank you for contacting Apple. My name is Manuel. What can I help you with today?
• Christopher: The iMac G5 I recently purchased is very loud.
• Christopher: Just wondering if this is normal
• Agent: Well not sure how loud that could be. Is it making buzzing noises?
• Christopher: Two things - a high pitch whine, or you might say a buzzing noise, and a noise that is more like some clicks - on occasion
• Christopher: I suppose 'loud' is a relative term, but my wife complains about the noise from the next room
• [...]
• Agent: What I'd like you to do right now is this
• Agent: I want you to turn the brightness of the screen up and down and then notice the intensity of that clicking sounds. user the keys F14 and F15 on the keyboard please
• Christopher: Well, that was interesting. Lowering the brightness lowered the amount of whining (buzz) but I didn't experience the clicking during the test
• Christopher: Raising the brightness raised the buzz back up again, BTW
• Agent: I'm going to transfer this chat to one of out specialist. It will take a minute or two
• Agent: Thank you for contacting Apple. My name is Ian. I see you're working on an issue with a prior Agent.
• Agent: http://www.apple.com/support/imac/assistant/wss/wss.html, could you try that link for me?
• Agent: I believe the condition that you are experiencing is related to the Power Supply
• Christopher: So what's the gist of the solution here? that I send the unit in for repair?
• Agent: no
• Agent: With the new iMac, it is completely serviceable by the customer
• Agent: Are you comfortable taking the computer apart?
• Christopher: yes
• Christopher: okay, i clicked through the link you gave me and it's asking me to sign in
• Agent: There are instructions and a tool included with the Power supply
• Christopher: It's giving me a dropdown menu to describe the problem - my problem isn't on the list
• Agent: Choose the closest item
• Christopher: Got it, ordering the part
• Christopher: So is this supposed to fix the clicking or the buzzing, or both?
• Agent: Yes, ordering the power supply will resolve this condition
• Christopher: Sounds like a known issue?
• Agent: If you are still experiencing this condition, please contact Apple Support by phone at 800-275-2273, reference the case number [deleted for privacy]

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