I suddenly remembered about degaussing. Not sure if it also made a noise when you did that.
For me the noises mention was from old CRT TV's. Would hear it randomly in the room when the TV was off as kid and would be like wtf...
I used to degauss every week. Not because I knew what it was for, I just felt like I should. Also jut got PTSD about a time I sat with my friend's dad and watched his 6.4GB HD defragging.