circuit diagram for reference. Fan normally sits with 5V on pin 1 and pin 2 is open (I assume pin 0 is not used). So both sides of fan should be at 5V when off. Inside the fan is a fancy circuit (I believe) that detects rpm and pulses the wiring accordingly with circuitry inside a chip inside the fan. I think the sound is coming from that circuitry trying to get the fan to start up but it can't because the voltage is too low.
What seems strange is that the fan is getting any power at all as I would think the firmware would keep Q1 turned off (when Q1 is turned on it grounds pin 2).
It could be that the firmware is not at fault and some part is broken (Q1 or D1 most likely) but I suspect it is a firmware thing where it is sending a small amount of power to the fan.
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Dim3nsioneer 558
You guys are sure it's the fan and not the enabled xy stepper motors? There I hear such a noise. But if I perform a homing through the menu, they are disabled and the noise gone.
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