AS3 Movieclip and Main timeline trouble

Hi all… im new here.
im having some AS3 trouble and was hoping you guys may know the answer.
im doing a sort of a website thingi on flash for one of my college projects.

i have the main menu buttons in the main timeline and the contents of every page inside movieclips. there is one movieclip which triggers a sound clip. what i want to do is to make that sound stop when someone navigates away from the page (that is for the sound to stop when a button in the main timeline is clicked)

anyone knows how to do it?