can you un-preload sounds?

What happens when you no longer need the sound that is preloaded via llPreloadSound? Is there a way to un-preload it? If I keep changing sounds (by user request) and preloading each one, will that just keep growing the number of sounds that are preloaded?

you um... clear your own cache .

http://wiki.secondlife.com/wiki/LlPreloadSound only caches the sound for/to viewers within range.
This data is not stored in the script and is not stored in the prim, it is just uploading data to anyone nearby once and filling THEIR cache and using their download bandwidth (once), it is viewer side and there is no undo.

I always thought that triggering many llPreloadSound() at once (apart from the 1sec delay) would be a pretty bad bandwidth flood, possibly unecessary filling caches, therefore
I always thought that using preloadsound just in time would be much more efficient, and i tested that with 16kB/s and found it better to: preload only the next sound just when the previous sound starts playing.

Is a preloaded sound stored in viewer memory or is it just cached?

The user would be selecting from available sounds, making the choice to hear the sounds, so I'm not worried about his bandwidth. Each will be preloaded as he selects it, the assumption being that he could leave the item in the state he's selected.

If listening to twelve sounds just means he's cached twelve sounds then that's fine. What I'd like not to happen, though, is for his viewer memory to have expanded to hold twelve sounds, eleven of which he doesn't need.

Twelve sounds being preloaded would be absolutely minimal compared to having to load twelve 1024x1024 textures AFAIK.