Simple question (maybe) about a looping MovieClip

I’m an experienced Flash developer, but virtually all of my experience is with pure AS3 coding in FlexBuilder or FlashDevelop. I know very little about Flash CS3, .fla files, timelines etc. (I do have Flash CS3 installed at least).

So I’m in the embarrassing position of having developed a game, sold a primary license, released it to the world and gotten additional sponsors asking for custom branded version and I can’t figure out how to add their simple MC intros correctly.

Specific problem: I have an intro clip from a portal that gets played by my preloader class (it’s embedded as an SWF and then added cast as a MovieClip) after the game is loaded, but before the main menu comes up. The problem is that the movie clip keeps looping. I’ve removed it from the stage, cleared all references to it and unset any event listeners, I can still hear its sound play over and over. So how do I tell this MovieClip, “Stop. You’re done, go away.”?