The cooler makes a terrible noise, what is the reason?

Question

Cooling systems

In general, the cooler of the main CPU has recently begun to make noise. The sound in general is - hrum-khrum-khrum.
The thermal paste was changed recently. The temperature of the processor does not even reach 30.
Dust wiped everything perfectly.
The funny thing is that when I remove the cover from the system unit. Everything is working properly. The cover or the cooler does not touch any wires there. I checked everything with a flashlight.

The only suspicion is that a gnome has wound up there, who begins to hamster his crackers.

Answer 1

Or touches something
Or the bearing is dead