setInterval gone wild!

programming
1

Hey guys. Was trying out setInterval, ive never used it before. I set it up to spawn a random ball every 3 seconds…but once the flash movie actualy PLAYS for the 3 seconds, then it calls the function every frame. Little help?

eSpawnInt = setInterval(eSpawn, 3000);
    function eSpawn() {
        _root.attachMovie("ballMC", "ballMC"+num, num, num++);
        _root["ballMC"+num]._x = random(550)+300;
    }
    clearInterval(eSpawnInt);