I'm not the authority on sound, but I do know of a couple functions that can help you out. Check out stopAllSounds() in your documentation.
What you can do is use stopAllSounds() in a preloader for your movie. Your code would look something like this...
tot = targMC.getBytesTotal();
cur = targMC.getBytesLoaded();
if (cur != tot)
What that will do is loop through three frames until your movie is loaded completely (don't forget to change the name of the movieclip to match). Once it is completely loaded, it will trigger the stopAllSounds() and continue through the timeline.
Hope that helps ya, comrade.