I was doing this in front of my PC and noticed that when I did it at a certain frequency my CRT image started to wobble a little bit.
So I practiced for a few minutes untill I found the harmonic frequency for my CRT - and guess what !!!
I blew the damn thing up and had to buy a new one.
Yep and I have tested - it works on all CRT monitors, If you hum or buzz at the right frequency it blows them up.