I'm dating myself here but I remember similar techniques back in the original IBM PC days to play sampled audio through the built-in PC speaker: https://en.wikipedia.org/wiki/RealSound
Accessing address 0xC030 (PEEK(-16336) or STA $C030) would cause the machine's internal speaker to click. I assume it was the result of the voltage to the speaker toggling from digital on to digital off.
POKE(-16336) was quieter. I figured it was because it was implemented as a quick read-then-write instruction sequence, too fast for the speaker diaphragm to move end-to-end (effectively a quieter sound). Assembly behavior was different.
In spite of its simplicity, there were games with amazing PWM sound effects (crude by today's standards, but magical in the early 1980s). The software company Muse even produced a sort of speech synthesizer that played sampled words, like an audio version of a ransom note. It sounded wonderfully awful.