Apple iMac making a lot of noise?
If your desktop iMac is making a lot of fan noise, something is causing your computer to get really hot. This could be down to blockages in the fan outlet channels, broken heat sensors inside your iMac or software processes causing a lot of strain on the hardware.
To see if you’ve got a process or app that’s causing the fans to kick up, first go to the magnifying glass in the top right of your screen and search ‘activity monitor’ open it and click the CPU tab and in the CPU% column you will get a read out of all the apps and processes being carried out by your iMac and the amount of computing power they’re using.
From thing you will be able to distinguish if you need to run certain programs individually with other apps closed and so on. Checking on the problematic apps to see if they have any new updates available is also a good shout.
If you’ve got your iMac in an alcove or on a closed shelf, try moving it out into the open so it can circulate the warm air out and cold air in. If they same air is being dragged through your iMac over and over again it will gradually rise causing your fans to work harder trying to cool off your Mac.
If none of these tips have worked, chances are you have a problem with a heat sensor in your Mac. The first port of call is to do a SMC reset. Do this by first turning off your Mac and unplugging it for 15 seconds. Then power on whilst holding these buttons: control+option+shift+power on
Talk to a Apple Repair Specialist
If this does not help. You will need to contact an Apple repair specialist who can safely open your Mac and replace the broken sensors and clean out any dust inside.