I was having similar issues with sounds and music. If you are using the Music Volume Trigger there are certain tracks that are considered "music" in the engine and can be stopped with the On Exit Play 'music_off' event. This does not work for some tracks and sound effects so instead use the Sound Volume Trigger and set the 'Ambient Resource ID' to the sound resource you want, it will by default stop playing the sound if they leave the trigger area. As far as scripting it to stop in osiris, i also had no luck with this....