Fan malfunction on new lattepanda sigma

Hi,

I have a new LattePanda Sigma that I received mid august.

Since a week the fan has started to make a strong buzzing/rattling noise after a few minutes of operation

I observed the BIOS to catch the behavior live on the recommendation of this thread : https://www.dfrobot.com/forum/topic/322966
In normal (low noise) operation it was reading around 2300 rpm at this temperature under this configuration.

When the heavy noise appears the fan speed drops under 1000 rpm for the same configuration and temperature.