mac mini mid-2010 fan spins up for a second, then stops

I have a mac mini 4.1 mid-2010 with High Sierra installed currently. Everything works perfectly, however I noticed that the fan is regularly spinning up for just a second, then stops again for several seconds and the cycle repeats. Trying to set a fan speed manually with macsfancontrol doesn’t change the behaviour at all. However the app seems to be able to read out the fan speed correctly, it shows 0rpm when the fan isn’t spinning and a few hundred rpm when it’s briefly turning on.
The fan is able to spin freely, there is nothing physically blocking it. What could cause this strange behaviour?
Thanks,
AK