If there is such a flash card, this sounds like the easiest explanation. Someone swapped the card with a file that starts with the real announcement, then X minutes of silence, followed by joke sounds.
Absolutely did this in middle school music class, where there was a cassette player that usually went unused. I don’t remember the details but it was basically 10 minutes of silence and then some raunchy audio, probably NIN or Marilyn Manson (it was 1998 and we were 12).
Especially if the crew is used to the player stopping automatically at the end of the spiel. The attendants wouldn't suspect the player because the earlier announcement ended so why would playback still be going?
