I've got some background noise of gunfire that I've placed on a separate layer.
The keyframe containing the gunfire is set to "Stream - Loop" so that it keeps
repeating while staying in synch with the timeline. Now when the scene changes,
I want the gunfire to stop. How can I do this? I tried placing a blank keyframe
at the end of the scene and setting the sound synch to "Stop", but that still
doesn't kill the noise. I also tried adding a "stopAllSounds();" ActionScript
to this blank keyframe, and although that stops the gunfire, it also mutes
every other sound in the following scenes. So how do I simply stop a sound-loop
when I want to?

You should try playing sound with actionscript. It's not hard at all.
http://livedocs.adobe.com/flash/8/main/wwhelp/wwhimpl/js/html/wwhelp.htm?href=00002872.html

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Sorry about that link. please use this link instead ....-_-"
http://livedocs.adobe.com/flash/8/main/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=00002687.html