Thank you all for taking the time to reply and thank you for your ideas.
I want to say that I never meant to imply that Windows 10 had simply "decided" to increase the speed of the CPU fan. Logically, if the fan was speeding up it was because the CPU was working harder, which made its temperature go up, and it was trying to cool it down. I wanted to determine what was the cause of the increase in CPU utilization, which caused the increase in temperature, which in turn was causing the increase in fan speed, and I said it was something in Windows 10 because it didn't happen in the other operating systems I had worked with.
I did try some of the things suggested:
* I had noticed before that Cortana is always using up some memory, even though I did not enable it when I upgraded. So I did what Nus said and changed its folder name to prevent it from running.
* I changed the "Updates from more than one place" option to OFF, as suggested by PRMan.
* I even disabled the Windows Update service completely.
* I tried looking for and updated graphics driver, as was suggested in another forum, but found none.
However, none of those things was the cause of the problem. Checking the Task Manager I found two background processes called:
From Microsoft Background Task Host
From Microsoft Download/Upload Host
These processes are both located in the C:\Windows\System32 folder and their files are backgroundTaskHost.exe and BackgroundTransferHost.exe, respectively. At the time of writing this I have no idea what they do or what they're for.
All I know is that, normally, the CPU use in my computer is under 10% and whenever these two processes pop up, CPU use jumps to as much as 60 - 80% and remains in that range, even if I'm not doing anything else. Then, when I kill the processes, the CPU activity decreases and, naturally, the fan slows down.
So, as much as I wanted to blame Cortana, she was not the wrongdoer... These two blokes are.
In any case, does anybody know something about these two processes? How to disable them or prevent them from running, maybe? Even after I kill them, they briefly pop up in the Task Manager from time to time.