I wasn't able to reproduce your issue. Your method "works" but setting them looping cause sound glitches. Here's a rewrite of the same code. I tested it with two different sounds and it works good for me. All I did was slap this and an AudioSource on a game object, together with two clips for the script. Instead of waiting for a timer I am checking until the sound stops. I don't use looping sounds (since this will do the loop by itself). Also I call audio.Stop() between each clip as you can see below, but I doubt it would do any difference unless you were waiting and using a looping sound (as you were originally).

// This code was tested and seems to run fine on my machine.

// Plays back one of the audio choosing randomly between them. 
var clips : AudioClip[] = new AudioClip[1]; 

function Start () 
{ 
    DontDestroyOnLoad(this);     

    audio.playOnAwake = false;
    audio.loop = false;

    while (true) 
    { 
        audio.clip = clips[Random.Range(0, clips.length)]; 
        audio.Play();

        while (audio.isPlaying)
            yield;

        audio.Stop();
    } 
} 

@script RequireComponent(AudioSource)

where here is the code im using now this one my uncle gave me (he is a programer for a living) and it still stops at four shots we know its not the script and it is not a audio listener problem because i only audio lister in the level

// Plays back one of the audio choosing randomly between them. 
var clips : AudioClip[] = new AudioClip[1]; 
function Start () 
{ 
    DontDestroyOnLoad(this); 
    audio.playOnAwake = false; 
    audio.loop = false; 
    var vvv =0; 
    while (vvv<0) 
    { 
        audio.clip = clips[Random.Range(0, clips.length)]; 
        audio.Play(); 
        while (audio.isPlaying) 
            yield; 
        audio.Stop(); 
        vvv++; 
    } 
} 
@script RequireComponent(AudioSource)

The conditional statement must be True for the while loop's code to be executed, but in your script there is:

  while (false)
  ... 

Edit: Maybe you should use this script and assign the clip when the player presses a button:

function Start () {
  audio.loop = true;
}

function Update () {
  if (Input.GetKeyDown (KeyCode.DownArrow)) //assign your key here
    audio.clip = ...; //your random function
    audio.Play();
  if (Input.GetKeyUp (KeyCode.UpArrow)) //assign same key here
    audio.Stop();
}

can't you just set it to loop in the inspector ?