When 27"Imac in in Sleep mode or turned off, slight crackling electrical noise?

[ejosepha]

When the computer is sleeping or if I turn it off but the plug remains in the electrical socket, when I get very close to the machine I hear a slight crackling noise, as if the internal adaptor is making a slight noise. I don't hear it from any normal distance, and other than the buzzing phenomenon when brightness is below 50%, no other symptom. Is this normal for this model. I believe that the external adaptor for the 30" ACD made a louder but similar noise as well unless unpluged.
Thanks

 

[adammjenkins]

Hello,
I am currently on my third 27" i5 iMac due to similar issues. The first one that I had made the exact noise that you are describing. I noticed it when the display was either dim, below 50% brightness, or off, and the noise persisted even if the computer was shut down. I called AppleCare, they organized a replacement for me. The second and third iMacs have had a very similar problem, only in reverse. On these past two, when the brightness is above 50%, I hear the buzzing and a high-pitched dog whistle noise coming from the upper left corner of the screen (it is most audible near the back vent for obvious reasons). I have been in contact with a senior advisor, and he just heard back from the engineers today. They have determined that it has something to do with the cable running from the power supply to the backlight, or the backlight itself. This iMac is going back, and I am opting for a refund and waiting until the next refresh to re-purchase it. I am just to the point where I think the issue is more widespread than anyone really realizes, and I don't think that another replacement is going to solve the problem.

My advice is to get in touch with Apple Care and get it diagnosed. Whether you choose to opt for a replacement or refund, well... the ball is in your court.

Please try to report back here on this thread if you get any more information from Apple Care regarding this issue.

 

[ejosepha]

I think my problems are separate, not the same.

I understand the issue of the buzzing on top left when brightness is decreased...which disappears when you increase brightness sufficiently. I am talking about something else though.
This slight electrical noise seems to be coming from deeper within the unit, which you would never hear unless you put your ear next to the top of the computer. It is more like the sound of an the electrical adaptor when the machine is turned off and it is handling the incoming electricity. Like the block outside the portable computers or, as I said, the 30" ACD.
I was just wondering if it is normal or not on this unit.
In terms of the buzzing sound on my unit, it only kicks in after the computer is one for 15 minutes or so, then the buzzing begins and can only be stopped by increasing brightness. Besides brightness, it seems linked to how hard the computer is working, or perhaps heat. I rarely do more than surf internet, and mail on it though and fans and temps remain quite low.
However, I don't hear this when directly in front of unit working, only when I stand up or move to the side of the unit.

 

[adammjenkins]

I haven't noticed the crackling that you've described other than the screen buzz. I can add, though, that the buzzing in my iMac also intensifies if the machine is working harder/running hotter. (For example, if I am ripping a dvd in Handbrake, which utilizes all 4 cores).

Sorry to not add much to your specific question, but the way that you described the issue made it sound like the buzzing noise associated with the screen brightness.