My Intel NUC has been running OpenBSD for about a year and recently I upgraded it to OpenBSD 7.1.
in-place upgrade of OpenBSD 7.1 was easier than FreeBSD 13.1
And out of the blue the fan started screaming or rather the fan was at 11. I think I rebooted a few times and it always started screaming. Finally I found a post that suggested that OpenBSD did not idle the CPU. Which might be true except the sound and temp was new. A different post suggested it was dust in the fan compartment.
Not having any compressed air I was forced to take the NUC apart and clean it as best as I could. Voila. No more screaming. My lab now hums with the drone of the A/C. (almost as bad).