Adding sound to an iOS app

I'm trying to add sound to an iOS app that I am writing. I keep getting the error message "Incorrect argument label in call (have 'contentsOfURL:error:', expected "contentsOfURL:fileTypeHint:')". I have tried tinkering with it in several ways, and I can't get it to build. Here is my code:

import UIKit import AVFoundation

class ViewController: UIViewController {

var Setup = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("DMSetup", ofType: "mp3")!)
var audioPlayer = AVAudioPlayer()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    audioPlayer = AVAudioPlayer(contentsOfURL: Setup, error: nil)
    audioPlayer.prepareToPlay()

}

override func didReceiveMemoryWaing() {
    super.didReceiveMemoryWaing()
    // Dispose of any resources that can be recreated.
}

@IBAction func PlayKeySetup(sender: UIButton) {
    audioPlayer.play()
}

}

Any suggestions? I'm a newbie at this, so I'm sure I'm missing something obvious. xCode 7.3.1, OSX 10.11.4

Thanks.