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.