When recording "notes to self" using built-in laptop soundcard & mic array and any audio recorder, the results include the cooling fan cycling on and off.
The fan is quiet by ear but on the recording you'd think it's the loudest thing in the room.
Fan cycles 4 min ON, 2 min OFF.
I had an old boom box cassette deck internal mic that would do the same thing recording motor noise.
This can't be normal?!
Sample: (silence - fan start/stop - silence)
lp fan (5).mp3