Unload and kill the sound of an external SWF

I have the following program to play a .flv movie on a webpage made by myself:

var Xpos:Number=0;

var Ypos:Number=0;

var swf:MovieClip;

var loader:Loader=new Loader();

var mySWF: URLRequest=new URLRequest("http://......./.swf");

loader.load(mySWF);

loader.x=Xpos;

loader.y=Ypos;

addChild(loader);

loader_btn.addEventListener(MouseEvent.CLICK, loaderClick);

function loader_btnClick(event:MouseEvent):void{

removeChild(loader);

var newSWFrequest:URLRequest=new URLRequest("http://......../.swf");

loader.load(newSWFrequest);

loader.x=Xpos;

loader.y=Ypos;

addChild(loader);

}

close_btn.addEventListener(MouseEvent.CLICK, close_btnClick);

function close_btnClick(event:MouseEvent):void{

SoundMixer.stopAll();

loader.unload();

bg_movie_mc.visible=false;

close_movie_btn.visible=false;

bg_movie_mc.stop();

}