title: Background music is playing twice
body: <p>When the view gets loaded on my menu (menuViewController) the background music starts (which works). Then when I click start and go to my game (GameViewController) and go back to menu (menuViewController) it starts playing twice.</p>
  
  <p>Here's my viewDidLoad()</p>
  
  <pre><code>override func viewDidLoad() {
      super.viewDidLoad()
  
      if x == false{
          setButtons()
  
          // get path of audio file
  
          let myFilePathString = NSBundle.mainBundle().pathForResource("Background Music Loop (Free to Use)", ofType: "mp3")
          if let myFilePathString = myFilePathString {
  
              let myFilePathURL = NSURL(fileURLWithPath: myFilePathString)
              do { try myAudioPlayer = AVAudioPlayer(contentsOfURL: myFilePathURL)
                  myAudioPlayer.volume = 0.4
                  myAudioPlayer.prepareToPlay()
                  myAudioPlayer.play()
                  myAudioPlayer.numberOfLoops = -1
              }catch{
                  print("error")
              }
          }
      }
  }
  </code></pre>
  
  <p>I tried instantiating the menuViewController and then using that instance instead of automatically creating a new one (which i guess didn't work)</p>
  
  <p>This is in my GameViewController</p>
  
  <pre><code>@IBAction func goToMenu(sender: AnyObject) {
      let storyboard = UIStoryboard(name: "Main", bundle: nil)
      let vc = storyboard.instantiateViewControllerWithIdentifier("menuViewController")
      self.presentViewController(vc, animated: true, completion: nil)
  }
  
  override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?)
  {
      if segue.identifier == "gameToMenu" {
          let destinationController = segue.destinationViewController as! menuViewController
              destinationController.x = true
      }
  </code></pre>
  
  <p>I also get an error that says:</p>
  
  <blockquote>
    <p>"Warning: Attempt to present Ninja.menuViewController: 0x7fdad4cdbf20 on Ninja.GameViewController: 0x7fdad1c1d7a0 whose view is not in the window hierarchy!"</p>
  </blockquote>