How to use a key as trigger?

I have added the Z key as trigger for an Audio Source (Zombiemusic) connected to a Third Person Controller. It works perfectly, and will start at key press, but when I start the game mode the Audio Sorce is already active and will not stop unless I press a key for another camera view (orbit cameras and a first person controller). How do I ensure that the audio source isn't playing at the start? This is my script:

public class CameraSwitcher : MonoBehaviour {

 public GameObject camera1;
 public GameObject camera2;
 public GameObject camera3;
 public GameObject camera4;
 public GameObject fpsController;
 public GameObject thrdController;
 public GameObject Zombiemusic;

 void Update() {
     if (Input.GetKeyDown ("1")) {
         camera1.SetActive(true);
         camera2.SetActive(false);
         camera3.SetActive(false);
         camera4.SetActive(false);
         fpsController.SetActive(false);
         thrdController.SetActive(false);
         Zombiemusic.SetActive(false);
     }

     if (Input.GetKeyDown ("2")) {
         camera1.SetActive(false);
         camera2.SetActive(true);
         camera3.SetActive(false);
         camera4.SetActive(false);
         fpsController.SetActive(false);
         thrdController.SetActive(false);
         Zombiemusic.SetActive(false);
     }

     if (Input.GetKeyDown ("3")) {
         camera1.SetActive(false);
         camera2.SetActive(false);
         camera3.SetActive(true);
         camera4.SetActive(false);
         fpsController.SetActive(false);
         thrdController.SetActive(false);
         Zombiemusic.SetActive(false);
     }

     if (Input.GetKeyDown ("4")) {
         camera1.SetActive(false);
         camera2.SetActive(false);
         camera3.SetActive(false);
         camera4.SetActive(true);
         fpsController.SetActive(false);
         thrdController.SetActive(false);
         Zombiemusic.SetActive(false);
     }

     if (Input.GetKeyDown ("e")) {
         camera1.SetActive(false);
         camera2.SetActive(false);
         camera3.SetActive(false);
         camera4.SetActive(false);
         fpsController.SetActive(true);
         thrdController.SetActive(false);
         Zombiemusic.SetActive(false);
     }

     if (Input.GetKeyDown ("z")) {
         camera1.SetActive(false);
         camera2.SetActive(false);
         camera3.SetActive(false);
         camera4.SetActive(false);
         fpsController.SetActive(false);
         thrdController.SetActive(true);
         Zombiemusic.SetActive(true);
     }
 }

}