iMac G5: Unexpected noises: Humming, buzzing, clicking

Several iMac G5s exhibit a humming, buzzing or clicking noise that is emitted from the included power supply. In most cases, users are able to obtain a replacement power supply that does not exhibit the noise problem, which Apple claims only affects 'AC-Bel' branded power supplies plugged into 220 volt outlets

Several readers have since noted ways in which this problem can be reproduced. In particular:

• Open iTunes. Without playing music, simply activate "visual effects" and enter full-screen mode.
• Play a QuickTime or other movie, or a DVD. Preferably, on a hard drive volume so potential DVD drive noise is eliminated
• Write a short C program or Perl program, or a shell script,
• that makes the CPU very busy. One reader writes "Just a while-forever loop in Perl does it."

Additionally, MacFixIt reader Doug notes a way to isolate and intensify the noise, should your iMac be affected:

"As some on the message board postings have noted, cupping my hand under the left hand side of the screen seems to 'focus' or intensity the noise. Actually, two foci, one 1/3 and one 2/3 from the central Apple logo to the left edge. Makes sense, since the CPU fan and CPU are on the left hand side (when facing the screen, naturally). [...] It's going back to Amazon, for a replacement, tomorrow. Love the speed, love the form factor, can't take the squeal."

Meanwhile, MacFixIt reader Trev reports that the "screeching" noise only occurs when two, separate applications simultaneously provide audio output:

"I've noticed that whenever I have music or have any other sound playing and then another sound plays like adjusting the volume alert or receiving an instant message I hear a scratching/hiss/scratching noise come from the speakers while both sounds are playing simultaneously. So if I'm listen to iTunes and I adjust the volume with the alert sound going off I hear the noise. If I adjust iTunes volume with it being the only sound its fine. If I adjust the alert volume by itself still no problem."

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."

Brightness setting affects loudness A number of readers also confirm that the brightness setting on their iMac G5 display correlates with the level of noise generated.

Chad Wadsworth writes "I also feel that my iMac 20" is too loud and have had a hard time isolating the irritation. The noise is definitely more of a high frequency hum that changes intermittently.

"I just woke the system from sleep so with the power save set to automatic, the system is now at its quietest mode yet I can still hear a faint buzz. I opened the display control panel. Here's what I found: Maximum brightness- distinct buzz, Minimum brightness - silent."

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]

It should be noted that a number of the above mentioned sounds may be resultant of normal operation and considered to "within spec" by Apple. Also, we've yet to receive a report of actual hardware failures occurring from any of the above noise issues.

Also, if you hear a blast of fan noise when using the Apple Hardware Test CD, don't be alarmed. All current G5 computers use a software-based cooling system that monitors temperatures at various locations inside the computer and activates and deactivates each fan individually as necessary to cool the machine. (Power Mac G5 computers have nine fans in total; the iMac G5 has three.) However, when booted from the Hardware Test disc (or when booted into single-user mode or FireWire Target Disk Mode), the necessary monitoring software is not running, so all fans are activated as a precautionary measure.

Finally, we've received a number of reports noting that fan noise is louder in 17" iMac G5 models (or at least that the fan runs more frequently) than in 20" models. Although this is speculation on our part, it seems logical that the smaller enclosure of the 17" model would require more fan action to keep cool due to the tighter space inside. The larger enclosure of the 20" model likely has better internal airflow.

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