Switch spins the fan loudly when in standby mode

I’ve heard some Switch’s have this problem of spinning the fan when in stand by mode (without being connected to a dock or charging cable). Any idea is this is a software bug or hardware related problem?

I will elaborate this problem a bit. I have a switch where the fan spins either in full speed or wont spin at all. It seems like the PWM control does not work. The switch hasnt been tampered before and there are no signs of liquid damage.

I tried another fan, checked the connector, changed thermal paste and compared the resistance values to a known board. Everything seems to be ok.

when I turn on the switch the fan starts to spin at the first boot logo and fan turns off when the screen turns off at the lock screen. When I wake it from sleep mode the fan goes to full speed

Any idea what causes this problem.

It has vanilla HOS

Some quick googling suggests that it’s not uncommon, but I can’t see anyone who has fixed it without just sending it away to Nintendo. I wouldn’t really know where to start, presumably the fan PWM comes directly from the CPU? I’m not sure where would be best to start…