"I would dial the 300 baud dial-up number, and scream the carrier tone."
I have a very low voice and enjoy singing or humming along with the bass line in music some times.  While I was singing along with a song, all of a sudden my monitor started to go a bit nuts and wave.  When I stopped singing (or changed notes) it stopped.I turned to my roommate, "Can you see that?""Nope."It turned out that if I sang a note at the same frequency as my monitor's refresh rate, the image on the screen would start to modulate up and down in a wavy sort of way.  But to my eyes alone.  Must have been something with the motion of my eyes or my head matching the refreshing of the screen.