Operation of these blowers (they are not fans!) below 25% duty cycle is not guaranteed to be reliable and is thus not recommended. In some cases, the blower may stall (stop spinning) and not react to a significant increase in heat in a timely manner. In addition, during the stall process, the blower may struggle to keep spinning and this can produce erratic sounds. In other cases (i.e. particular blower models), duty cycle values below 25% are actually ignored and the blower will continue to operate at its minimum (25%) duty cycle.
My recommendations for the CPU Fan Header settings - which, BTW, differ from the shipping default configuration (which I consider downright buggy) - are as follows:
Minimum Duty Cycle (%) 25
Minimum Temperature (°C) 60
Duty Cycle Increment (%/°C) 3
Hope this helps,
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N.Scott Pearson, thank you for your valuable help.
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Well, I guess there is no option to further reduce the noise in idle and in light work ?
At 25%, you shouldn't be able to hear the blower unless you are within a foot or two of the unit.