Keyboard error sound in Windows 10 when stimulating invalid matrix positions

[THX1138]

I wanted to add some keys to my PS/2 keyboard. The controller has eight rows and 16 columns but the keyboard has 102 or 103 buttons (not sure) so that leaves 20-something matrix positions unaccounted for. I used a breadboard jumper wire to connect the rows and columns in sequence and found five usable vacant matrix positions. I also found a lot of whatever this is; some kind of error? It's what I came to ask about. Does anyone recognise this sound? When I make a quick contact with the jumper wire, I get two beeps but if I hold it down for longer, I can get a bunch of beeps. The sound comes from my proper speakers, not the motherboard piezo thing. Please disregard the image in the below video; it's just what happened to be on my screen when recording the sound. Is the keyboard in distress when I do this or what? Does any other situation cause this sound?

I'm using Windows 10.

[nnnik]

For the youtube embed thingie to work you need a youtube link like https://www.youtube.com/watch&v=zvTZgzK3jTE