@vergiliszta Thanks for your comment and additional investigation. Your scope image is exactly the same as I measured.
I replaced the 10uF capacitor with a 10nF capacitor
Interesting, I did not measure the capacity C1 and is a good candidate to remove as experiment. I remember the fan current is around 100mA @5V full speed.
The PWM duty cycle is hard-coded in the MT006C6PB (STM8S003F3) microcontroller, so that cannot be changed. It converts I2C value 1…100 to 30%…100% PWM.
Note: I did not use the Argon scripts like argononed.py, but direct I2C commands to control the fan speed:
# Value 0..100 to set fan speed:
$ i2cset -y 1 0x01a <value>
So far zero feedback from Argon One support which is not good. I did not solder on the board to claim warranty, but I don’t see a reason for RMA when you reported the same issue. It looks like a design or production fault which is not confirmed by Argon yet.