Audio How to manage AudioSources at runtime

Hello.
I'm trying to do a music application in Unity.

I have a problem when I apply a fadeout to mute the sounds that are being created to don't have clicking when they stop.
All the music that is in the background also enters into the fadeout. I would like to be able to do fadeout without interfering in the background music, but i don't know how. This is my code:

Code (CSharp):

1. private AudioSource[] sound;
2.  
3. void OnTouchDown()
4. {
5.  
6.     if (instrument == "Piano")
7.     {
8.         FindObjectOfType<PianoAudioManager>().Play("PianoGmaj1G");
9.     }
10.  
11. void OnTouchUp()
12. {      
13.     sound = FindObjectsOfType(typeof(AudioSource)) as AudioSource[];
14.     foreach (AudioSource audioS in sound)
15.     {
16.         StartCoroutine(AudioFadeOut.FadeOut(audioS, 0.02f));
17.     }

How could I save the sound when I activate it so I can do the fadeout without affecting everything else? I have been stuck with this for days and I can not find how to do it. I would be very grateful for any help. Thank you

My PianoAudioManager code is:

Code (CSharp):

1. public class PianoAudioManager : MonoBehaviour{
2.  
3. public PianoSound[] PianoSounds;
4.  
5. public static PianoAudioManager instance;
6. public AudioMixerGroup PianoMixer;
7.  
8. void Awake()
9. {
10.  
11.     if (instance == null)
12.         instance = this;
13.     else
14.     {
15.         Destroy(gameObject);
16.         return;
17.     }
18.  
19.     DontDestroyOnLoad(gameObject);
20.  
21.     foreach(PianoSound s in PianoSounds)
22.     {
23.         s.source = gameObject.AddComponent<AudioSource>();
24.         s.source.outputAudioMixerGroup = PianoMixer;
25.         s.source.clip = s.clip;
26.  
27.         s.source.volume = s.volume;
28.         s.source.pitch = s.pitch;
29.     }
30. }
31.  
32. public void Play (string name)
33. {
34.     PianoSound s = Array.Find(PianoSounds, sound => sound.name == name);
35.     if (s == null)
36.     {
37.         Debug.LogWarning("Sound: " + name + " not found!");
38.         return;
39.     }
40.     s.source.Play();
41. }
42.  
43. }