I will admit that i don't know a whole load about mac osx and the ins and outs of the mac environment Yesterday i thought i would try out macos sierra on a virtual machine to see how it works and figure out if my apps that i use support it. i didn't quite get that far. I got the sierra downloaded and then did a force quit on the install app that started up after the download completed. then from that point onwards my iMac fan when into hyperdrive. I took a look at Activity Monitor and there are 4 apps that seem to be chewing up cpu cycles and that is likely what is heating up the cpu and driving the fan. UserEventAgent 82.5% launchd 81.4% cfprefsd 36.1% mds_stores 29.4% i called apple support as i have applecare and they thought it was becuase of timemachine and it running. but if i turn off timemachine the apps dont stop and the the fan is still in hyperdrive. i can shut down the imac and wait 2-3 minutes and the cpu does cool down a bit. when i power up it's fine for about 3-9 minutes and then those procesesses kick back in and the fan goes back to full bore i called back apple care again and the sr support agent (who came across as an arrogant A!) insisted that it was an external device that is plugged into the iMac. Apart from my keyboard and some lightning connectors the only other thing that i have plugge in is my Lacie 3tb drive via thunderbot. I tried ejecting it and the processes calm down and the fan will slow. Remount the Lacie, and the problem comes back. He suggested that it's the drive that is failing. Is this a common thing? would re-formatting the drive fix it? i have gone into recovery console and did a fix on the Lacie and it says it can't find anything wrong. I don't want to be working with a red herring and replace a drive that was not faulty. Apple seems to take the approach of wipe everything and re-install rather that diagnose the problem. the first call was convinced it was timemachine. what would be the best steps to figure out why this fan is just ramping up into sonic jet mode?