Same 555 timer based PWM controlling a cheap box fan

[handsfreekvm]

Hello nice vid. did you make the PCB board yourself?

To get rid of the choppy sound during low duty cycles, you will need a higher frequency PWM signal. if you go higher in PWM frequency, 20Khz (above human hearing) it will eliminate any audible switching noise. so instead of (_|----|____|----|____) it would be (_|--|_|--|_|--|_) not to scale but basically the same average power during one x time frame but more pulses in that time frame.