public class PlayNotes : MonoBehaviour
{
    public AudioSource adSource;
    public AudioClip[] adClips;

    // Index of the currently played sound
    private int index;

    public void PlayNote()
    {  
        // Play current sound
        // I would rather use PlayOneShot in order to allow multiple concurrent sounds
        adSource.PlayOneShot(adClips[index]);

        // Increase the index, wrap around if reached end of array
        index = (index + 1) % adClips.Length;
    }  
}