What you hear is the horizontal refresh rate, scanlines per second. For NTSC television and CGA video, that's 15.7 KHz and within the audible range of quite a

What you hear is the horizontal refresh rate, scanlines per second. For NTSC television and CGA video, that's 15.7 KHz and within the audible range of quite a few humans. 640x480x60fps noninterlaced VGA is twice that at 31.4 KHz, which mostly isn't audible although a very few exceptional cases might. Higher resolutions are higher still, of course. That said, as with anything involving analog frequencies, there might be harmonics or resonances that could be in a range you can hear.