Audio repeating rapidly.

So I've been trying to add a specific audio clip to certain animations using C#. So far no luck. I have one placed in my fixedupdate so it would constantly play and another in my update void so it will only play when I hold down the space bar.

public AudioSource au_flying;
public AudioSource au_driving;

void Start()
{
au_driving = (AudioSource)gameObject.AddComponent ("AudioSource");
AudioClip DrivingClip;
DrivingClip = (AudioClip)Resources.Load("SFX/driving");...

Audio repeating rapidly.