volendo puoi elimiare l'array facendo cosi':

function loadExternalClip()
{
var indiceClip : Number = random(3);

var container:MovieClip = createEmptyMovieClip("container", getNextHighestDepth());
var mcLoader:MovieClipLoader = new MovieClipLoader();
mcLoader.addListener(this);
mcLoader.loadClip(indiceClip+".swf", container);
}

var intervalID = setInterval(this, "loadExternalClip", 2000);