Sound won't play at a specific time in unity - audio

Question

I am trying to make a sound play with the timer goes to 3, 2, 1.
My timer starts at ten and has a three second delay. If I use the following code:
if (tl.myCoolTimer == 10)
{
print("Play Sound");
myAudioSource.Play();
}
It plays the Beep over and over again until the game starts and the counter goes below 10.
If I use the code:
if (tl.myCoolTimer == 3)
{
print("Play Sound");
myAudioSource.Play();
}
It doesn't play the sound at all. It doesn't even print the print statement.
I literally only changed the number. I am not sure why this isn't working.
I have also tried setting it to 3f to see if it is a float issue.
Timer Scripts
This is the starting Timer. it counts down to 3 (then the game starts)
public Text startGameTimerText;
public float startGameTimer = 3;
public void Start ()
{
startGameTimerText = GetComponent<Text> ();
}
public void Update ()
{
startGameTimer -= Time.deltaTime;
startGameTimerText.text = startGameTimer.ToString ("f1");
if (startGameTimer < 0) {
GameObject.Find ("GameStartTimer").SetActive (false);
}
}
This is the Game Timer It starts at 10 and counts down to 0.
public StartGameTimer gt; //this is the script the other timer is on
public Text timerText;
public float myCoolTimer = 10;
public void Start ()
{
timerText = GetComponent<Text> ();
}
public void Update ()
{
if (gt.startGameTimer > 0) {
myCoolTimer = 10;
} else {
myCoolTimer -= Time.deltaTime;
timerText.text = myCoolTimer.ToString ("f1");
}
}

Answer 1

Thanks Joe for the help. Here was my final answer. I know it is hacked, but I haven't figured out the Invoke thing yet. When I set the into it kept playing the entire time it was at "3", so i need to make it play only once.
private AudioSource myAudioSource;
public bool isSoundPlayed;
void Start()
{
myAudioSource = GetComponent<AudioSource>();
isSoundPlayed = false;
}
void Update()
{
if((int)tl.myCoolTimer == 3)
{
if (isSoundPlayed == false)
{
myAudioSource.Play();
isSoundPlayed = true;
}
return;
}
if ((int)tl.myCoolTimer == 2)
{
if (isSoundPlayed == true)
{
myAudioSource.Play();
isSoundPlayed = false;
}
return;
}
if ((int)tl.myCoolTimer == 1)
{
if (isSoundPlayed == false)
{
myAudioSource.Play();
isSoundPlayed = true;
}
return;
}
}