I have a 27" iMac with 3.06ghz processor 1tb hdd and 4gb of ram purchased around march and I am having a weird problem with the hard drive fan. I brought it to the genius bar and they said the problem was with a program i was running(I dont believe them). I find the problem to be strange. I keep my computer running all the time and restart from time to time but rarely shut down. I noticed that the fan was running at high rpm's and they only solution was to shut down and restart would do nothing to resolve the problem. Then I noticed up in the next week that the same problem was happening. I started noticing a trend it was happening at the same time every week on the same day. I look up if there is anything in Activity Monitor causing the problem and I find nothing. Currently the only apps I have running mostly are Google Chrome, Mail, Adium, Itunes, Echofon and Dropbox. I wouldn't think that any of these apps are causing this problem. Anyone have any idea what could be causing this problem? Any help will be appreciated.
My guess is it sounds like a software problem. I think you might be on the right track finding out what is by using Activity Monitor. When the fan speeds up open AM and check to see what is using the most CPU cycles, if you see something taking up quite a bit that is probably the offending application. Any one (with the exception of Mail & iTunes) could be causing the problem.
Have you tried resetting the SMC? Also, I'm going to side with the Apple people if you're using some program to try and control the fan speed. That's just not a good idea. If it's just monitoring fan speed, then I'll be on your side saying it's unlikely to be the cause of the problem.
But resetting the SMC is the first step in troubleshooting here. If that doesn't fix it, you will have to get a little more forceful. In my experience, the "Genius Bar" seems more interested in finding some excuse to get you right back out the door if you're not going to buy something or it's going to take more than 5 minutes.
In addition to Roger and Scott's great input, I've also seen a few folks come thru here with real 1TB HD temperature sensor issues. Download the iStatPro widget and periodically monitor your temperature stats, then the next time the fan(s) kick up compare those temperature stats.
I have the same imac (3.06, 27 inch, etc) and I have two logic boards replaced plus one graphic card and still have issues with the load fan noise... I am tired of "sending it in" for service... It has been a problem since the first 60 days of purchase... My graphics card was replaced because I had an issue with my screen mirroring itself... what was on the bottom was also on the top of the screen. I have to take it in again on Wed ... so we will see. They said that if it happens again they will discuss about replacing the unit... I personally don't want it anymore with all the troubles... I would take a i5 or i7 though and just "deal" with the issue if it occurs.
I reset the SMC and did not resolve the issue. So I took the action to do a reformat and reinstall the OS figuring this would clear up and third party software related issues. Waited a week and the same thing is still happening. Really dont get why or what is causing this to happen its not like the HDD is running hot or anything according to istat. I called Apple Tech Support and will be bringing it in to a Authorized Repair center because my Apple Store keeps giving me the same story.
I have a 21.5" iMac that is doing the same thing. Every week I have to shut down the computer and restart it because it's fan goes into overdrive. I've had mine for almost a year now (purchased it in January 2010. It's driving me crazy too. I have tried resetting the SMC and that doesn't help. Every week without fail it happens. I have even left it running with NO programs running and it still does it.
I purchased my iMac in december last year and the noise of the fans drove me crazy. I finally found a solution which is kindof techno but now I at least have a nice iMac that I can enjoy in silence.
The thing is to slow down the harddisk fan rotation speed. You can do that by using a program called smcFanControl to set the maximum speed of the fan. The GUI of smcFanControl doesn't allow you to do that, you'll have to do it in a terminal window.
In a terminal window do the following:
For example, this will set the maximum RPM of the HDD fan to 2750.
The -k parameter is the HDD fan for the iMac. The -w writes the value of the RPM which is the hexadecimal representation of 4 times the RPM (i.e, 4 x 2750 = 11000 which is 2af8 in hex representation). Don't ask me why, but that's how it works.
I noticed that you have to run that line above each time you log in, so you might have to automate it.
Confirmation - the fix as posted works on my 27 inch iMac. My problem appears to be the same as others here, the HDD fan ramps up around 4500 RPM at 0300 in the morning. It appears to happen only every couple of weeks, maybe? Rebooting the box also resets it.
I have also found another workaround. I have not tried the smcFanControl yet but I went under the system preferences and went to energy saver and scheduled my computer to shutdown every week on the same day and then start back up about 15 min later. It's not a fix but definitely a way to get around it.
I am afraid to have the same. It started however with something different. About two months ago it started that my iMac spontaneously just switched off while working. I go only got it back on again by some reset procedure. After this happening 3 times I brought it back to the store for service, this was within warranty.
After a repair of 4 weeks with a new logic board (HD was said to be ok) I got it back at my home. All fine, could get it nicely on my network. However settings couldn't be saved anymore (e.g. deleting a network or switching the DHCP server) and I couldn't connect to internet. Network fine, some dns resolution but no internet. The helpdesk could only conclude that it "needed to go back to the doctor again". This was within 4 hours. After another 3 weeks I have it back now with a new HD - which is 1 TB where the previous was 500 GB - after about 15 minutes of simple work (Safari, some mailing) it starts to make a noise whether it is ripping a DVD. Very frustating given the history, I love my Mac for it's design but this is really bad.
i tried copying your "/Applications/Utilities/smcFanControl.app/Contents/Resources/smc -k F1Mx -w 2af8" code into terminal, but i get a reply saying that
"-bash: /Applications/Utilities/smcFanControl.app/Contents/Resources/smc: No such file or directory"
is copying the code above into terminal the right thing to do or am i doing it wrong? i have the latest version of smc (2.2.2)
I have a 27 inch quad core imac with a 2Tb Hitachi drive, had it from brand new since late october and noticed from the very start that after being switched on and booted up, the hard disk fan will start reasonably slow and quiet and gradually get faster and louder, 15 minutes will pass and the hard disc fan is running at 5000 rpm and is pretty loud, even though only running safari! Temperatures look ok at about 35 - 40 C all the time. the fan will run at 5000rpm until the imac is put to sleep or rebooted, when booted back up again, the process starts over again.
its always been pretty annoying but thought that was just something to do with having a quad core, but after reading up on it and seeing that it should be running fairly silently unless really stressing it, i know something isnt right.
anyone with any experience of this and getting it fixed in the UK? really cant have it sent to apple for them to poke at it for a few weeks, mainly because i cant afford the time without it with final year uni work deadlines looming, and the sheer heft of the thing getting it to a shop without a car. Really dont want to just get it swapped either as loading back all my applications and work will probably take longer than actually just getting the thing fixed!