This happened to my girlfriend and me twice on Messenger. On two consecutive nights, we heard a male voice with an American accent speaking as if he were talking to someone else, almost like they were conducting some kind of operation. It seemed as though he suddenly realized that we could hear him, after which the voice abruptly disappeared. The following night, it happened again, but this time the voice sounded like that of an African American woman. The situation was similar to the previous night. From that night, we have not used it to communicate and used Signal instead.
I work on products that feature live monitoring capabilities. There's no connection to the monitoring side's microphone (or camera) — why would there be? I'm not sure why there would be for their products.
Whatever the cause, it sure sounds like it was a strange and unnerving experience.
One time when I was in Hawaii I could swear there was a club playing dance music quite loudly somewhere a few blocks over: there was that muffled quality to it where I kept trying to pick out the song from inside my Airbnb.
Walking outside (after asking my wife if she could hear it): silence. Trees rustling, normal noises.
It was background noise. But inside the apartment that combination of different sounds was just right that it sounded like muffled music to me - but hence why I couldn't identify it, whatever was there was just me thinking I was hearing things.
Draw ones own conclusions about the relative technical plausibility of the events described by the OP (how would digital packet based audio experience a glitch which is structured as though you'd tuned into another analog radio station? It wouldn't: that doesn't happen and it isn't even a failure mode).
