iMac HDD fan running full speed. What is wrong? My iMac (27&quot; Mid-2010) and the HDD fan is spinning full speed with a measured HDD temperature of 50 °C. I have removed the dust and dirt from inside and it is pretty clean. Nevertheless even when at idle it starts at 48 °C.
I've tried to use software to control the fans in order to decrease temp but the lowest it gets is 47 °C. I checked every single connection inside and everything seems to be ok. I also tried resetting the SMC and PRAM but with no luck.
Specs

27&quot; Mid-2010
2.93GHz
Stock HDD 1.5TB Seagate st1500dl003
OS X Mavericks 10.9.4 and Windows 8.1 under Boot Camp
Looks like the drive experiences overheating issue. Unfortunately it's a common issue for Seagate drives which happens with time (had exactly the same problem with iMac 2010 21.5`` and stock 500 GB hdd). I used free Macs Fan Control tool to cool down the HDD (specially in Boot Camp, where the drive was even hotter). The article is about HDD replacement but it also explains how to use the app.

But the best solution I think is to replace the drive with some 2.5`` drive. They are known to be much cooler and quiter (though slower)