Audio clicking sound when switching between audiosources?

Hi,

I've been trying to fix the clicking sound that occurs when I abruptly switch between audiosources with a coroutine to fade out the sound:

Code (CSharp):

1.     IEnumerator VolumeFade(AudioSource idleUW, float _EndVolume, float _FadeLength)
2.     {
3.         float _StartTime = Time.time;
4.         while (!idleUW &&
5.              Time.time < _StartTime + _FadeLength)
6.         {
7.             float alpha = (_StartTime + _FadeLength - Time.time) / _FadeLength;
8.             // use the square here so that we fade faster and without popping
9.             alpha = alpha * alpha;
10.             idleUW.volume = alpha * .3f + _EndVolume * (1.0f - alpha);
11.  
12.             yield return null;
13.  
14.         }
15.  
16.         if (_EndVolume == 0) { idleUW.UnPause(); }
17.     }

I then activate the coroutine :

Code (CSharp):

1.   if (rb.transform.position.y <= -1.45 && !Input.GetKey(KeyCode.W))
2.         {
3.                 StartCoroutine(VolumeFade(idleUW, 0f, 0.5f));
4.  
5.                 idleUW.enabled = true;
6.        
7.             speed1UW.enabled = false;
8.             speed2UW.enabled = false;
9.  
10.         }

But it doesn't stop the clicking. Does anybody know how to fix this?