Alternatively:
You could get all your sound files that you want to pick from in the library and right click and add select linkage. Then tick off the export for action script and name them beep1, beep2, beep3....beep7, respectively.
Then go to the main timeline and add the code:
bgSound1 = new Sound(this);
bgSound1.attachSound("beep1");
bgSound2 = new Sound(this);
bgSound2.attachSound("beep2");
bgSound3 = new Sound(this);
bgSound3.attachSound("beep3");
bgSound4 = new Sound(this);
bgSound4.attachSound("beep4");
bgSound5 = new Sound(this);
bgSound5.attachSound("beep5");
bgSound6 = new Sound(this);
bgSound6.attachSound("beep6");
bgSound7 = new Sound(this);
bgSound7.attachSound("beep7");
Then go to your button and add:
on (release) {
soundplay = Math.ceil(Math.random()*7)
_root["bgSound"+soundplay].start();
}
Walla!