2 Loud noise from top of iMac 27" 2009, gets louder with brighter screen
This is regarding a iMac Intel 27" EMC 2374 (Late 2009, Core i7 2.8 GHz, 16gb Ram). I had the logic board changed by professionals about 4-5ya due to a malfunctioning processor.
The noise started appearing about a year ago, maybe during demanding tasks, but it would go away when the computer had time to rest a bit. Now it starts the moment the computer is turned on and shows no mercy.
Describing the phenomenon:
The sound is emanating from the top of the computer, slightly to the left (while facing the screen). From what i have read, this indicates that the PSU should be the culprit..
It can be described as a loud humming and hissing, like a classic fan but also not really…
It is loud enough to be unbearable when the screen is set to minimum brightness and it gets louder the brighter i set the screen. It starts of at maximum loudness when i turn the computer on and then backs down to the “brightness level” when everything is booted up.
It is not very static but does not clearly display a correlation between itself and cpu load.
Another strange sound appears, from the same spot, when the computer is shut down. As long as the power chord is plugged in there is a faint, cyclic, crackling sound. It grows slowly for about a second and then fades again as quickly, sort of a “kkrrrrrrrk” noise. After a couple of seconds of quiet it repeats. This goes on for at least 30 minutes after shutdown. It’s not a very loud thing but it can be heard clearly from a meter away. To me it sounds like a power transformer acting up. (My spontaneous thoughts go to capacitors/inductors having fun juggling charges??)
When the cycling crackling has gone i can hear a slightly worrying fizzing, crackling, humming, if i put my head close to the source. I know it’s super normal for transformers to make noise like that but from my experience they tend to be more high pitched and “clear”, whilst this is fairly grainy and irregular.
The computer runs fine, maybe a little sluggish during bootup but nothing unexpected from a 2009 machine.
I found this video of a guy with the same (if not very similar) issue who apparently fixed it by changing his PSU:
https://www.youtube.com/watch?v=wFc39ZIi...
But i also read people describing how their noises of the same nature returned soon after changing their PSU. So i’m suspecting there might be another underlying force at work here. And i would rather not buy a new one to have it bust after a few weeks. Or worse, ruin my machine while installing it ;)
I have installed Macs Fan Control and that shows no fans running at concerning speeds (3 displayed fans at slightly below 1k RPM at most), nor is any component specially hot (all displayed at under 60c)..
A huge thank you to anyone who read through this whole thing and I will love you if you can help me out with it!
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and oh yeah! I have tried using different outlets and turning of all other power in my apartment but there was no noticeable difference.
из Rasmus Booberg
The one thing that can make a mess here is bad power and/or ground! I would get a simple go-no go tester at the local hardware store like this one 3-Wire Receptacle Tester. It the outlet looks good you'll want to check the breaker panel ground connection. You should have a green or bare heavy wire which either ties to a clamp on your water pipe (metal) or to one or more ground rods. Make sure your connections are metal to metal with no corrosion build up.
Lastly, talk to your power company to have them plug in a recording power meter to see what's happening with the power.
из Dan
@danj since i have tried completely isolating the computer in its own power phase and comparing that with having it plugged in to a split with several lamps and other electronics. This gave absolutely no impact on the phenomenon. I also live in a newly renovated, state-owned, apartment in Stockholm and the electricity should really be of a high standard. What i have found working to some degree is unplugging the computer and holding the power button for a while. This apparently empties the PSU of charge. And then never letting it be plugged in while turned off, but rather have it go to sleep mode.
из Rasmus Booberg