The new version 2311003 of the Argon One (V2) fan control software appears to be buggy:
The ‘argononed.py’ script, which runs as a daemon, takes into account not only the CPU temperature, but also that of the external HDD to regulate the fan speed. As soon as the hard drive’s temperature rises above 30°C, the fan starts up and runs at 30% of its maximum speed (=very loud!).
In addition, the fan cannot be switched off with the FANOFF parameter. It will restart automatically after a few seconds.