It is actually very easy to reproduce for me, it happens whenever the temperature sensor is around 40°C, which is the fan activation threshold.
I got in touch with support and they asked me to kindly provide a video of the issue with a removed input cover, zoomed in on the fan. They would like to see the fan turning on at high RPM and immediately down again on the video.
I do not have time to do these experiments right now, but if anyone here has the time, please upload the video to YouTube and send a link here, and either send it to support or I would forward it to support myself!