Played Q*bert with my 5 years old yesterday and of course, he made his Q*bert fall out of the grid.
When the knockers knocked, my kid naturally said: "Q*bert fell at the bottom of your cab" and he started looking down.
BUT OF COURSE!
That sound is clearly supposed to emulate the sound of the little characters falling from the grid all the way down and hitting the bottom of your cabinet.
I bet if you open the backdoor right after a game, you can see a few Coilys and Q*bert knocked down lying next to the power supply.
After all these years I finally got it
WHAAAAAAAAAT you're kidding right, you didn't know that ?
From Wikipedia:Following a suggestion from technician Rick Tighe, a pinball machine component was included to make a loud sound when a character falls off the pyramid. The sound is generated by an internal coil that hits the interior of a cabinet wall. Foam padding was added to the area of contact on the cabinet; the developers felt the softer sound better matched a fall rather than a loud knocking sound. The cost of installing foam, however, was too expensive and the padding was omitted.
I tried to recreate the original intended sound a bit by putting some foam on the knocker....