Random number each time on javascript loop

Im trying to play a random audio file using howler.js and then reselect a different random file overtime it loops. I have it playing and looping but with the same file every time it loops. The only random selection is on initial load.

This is what I have:

    var number = Math.floor((Math.random() * 3) + 1);
    var sound1 = new Howl({
      src: ['audio/'+number+'.wav'],
      autoplay: false,
      loop: false,
      volume: 1.0,
    onend: function() {
    sound1.play()
     }
     });

sound1.play()

This happily plays one of 3 random wav files from audio folder but only selects randomly on load. The same file then loops infinitely.

Pretty new to javascript so any help appreciated. Thanks.