Question CPU (?) fan randomly going max speed

Apr 8, 2021
Hi all, I’ve had an on and off problem of a fan in my dell desktop (which I believe to be the CPU fan) suddenly going full speed during idle. CPU temperatures look normal during idle (with Firefox open) at around 40°C yet the fan will randomly rev up and sometimes maintain full blast for minutes. The sound is louder than I’ve ever heard my PC. I first ran into this problem a few months ago when the fan randomly started producing a loud roaring sound and would not stop until I shut the PC off. Eventually I checked the insides of my PC and cleaned some dust out of the heat sink and CPU fan, reapplied thermal paste, and put it back together. My problem then seemed to be solved for a few months until today when the roaring came back. Some days it will go without acting up at all but it always comes back eventually. Does anyone have any advice about how one would go about solving this? Let me know if I should post any additional information

Here’s a video that captures the sound: link