I am observing the same thing. It is happening when the local sensor temperature is around 40°C, which is the threshold for fan activation. However, sometimes it turns the fan on silently, keeping it around 2500 rpm, and sometimes it seems to spin up a lot only to reach the fan off threshold immediately and turn them off again. This then results in the weird on/off pulsating behavior.
There might be 2 problems at play at the same time:
- The fan is temporarily set for a higher RPM than it should be (way above 2500 rpm, which would correspond to the 40-41°C).
- The EC needs to use a higher hysteresis. I think they use a 0.5°C right now, which is simply not enough. In other laptops, the fans usually turn on and off at very different temperatures, e.g., turn on at 45°C and turn off at 40°C. This would solve the constant pulsating as well.