It might be that your internet connection is weak, affecting the music playback. Or, it could be that the music you chose isn't compatible with Instagram stories for some reason.
It's possible that there is a problem with your device's audio output. Check if you have any headphones or Bluetooth speakers connected. If so, ensure they are working properly. You can try disconnecting and reconnecting them. Also, test the audio with other apps or media on your device to see if it's a general audio problem or specific to Insta stories.
It could be that the volume is turned down too low or muted. Have you checked those settings? Also, the file might be corrupted or not compatible with the player you're using.