When you play a sound file, for instance, a vocal description when popping up an image (eg. playsound(tour, "something.mp3"), it doesn't actually start playing until the file is fully loaded into cache. What if the viewer leaves the event/popup that called the sound file before it starts playing? You don't want to have it start a second or two later. stopsound(tour) doesn't work since the sound hasn't started. destroysound(tour) causes an error since the sound doesn't exist, yet, apparently. I tried to supersede the unplayed sound with another using the same id, such as playsound(tour, "silence.mp3") but that didn't work.
So, how do you stop a sound before it starts paying?
Note: streamsound() may be an option but unless there is a solution to the above, you have to conclude that playsound() can almost never be safely used. Preloading all the sound files isn't a great solution. Say you have 50 voice-over files and which is played first is entirely random. If the viewer picks one that hasn't been preloaded the wait before starting could be even worse, by my understanding.