Getting weird effects from audio clip

The first problem is when the audio clip plays. I just want it to play when a unit/units are selected. However its playing every time I release the left mouse button?

using UnityEngine;
using System.Collections;

public class Unit : MonoBehaviour
{
	
	public Projector lightRing;
	public AudioClip YesSir;
	public bool selected = false;

	void Start()
	{
		lightRing = GetComponentInChildren<Projector>();
	}


	private void Update()
	{
		if(renderer.isVisible && Input.GetMouseButton(0))
		{
			Vector3 camPos = Camera.main.WorldToScreenPoint(transform.position);
			camPos.y = CameraOperator.InvertMouseY(camPos.y);
			selected = CameraOperator.selection.Contains(camPos);
		}

		if(selected)
			lightRing.enabled = true;
		else
			lightRing.enabled = false;

	
		if(renderer.isVisible && lightRing.enabled == false && Input.GetMouseButtonUp(0))
		{
			ConfirmCommand();
		}
	
	}

	private void ConfirmCommand()
	{
		audio.PlayOneShot(YesSir);
	}
}

The 2nd issue is the more Units I select the quieter the sound clip plays! (one or two units is fine, 3 - 5 its barely audible and 6 or more and you just cant hear anything)

Why is the volume apparently being shared between the number of units?

Any ideas please guys ???

Change lightRing.enabled == false; to lightRing.enabled == true;. U needed to play sound when char are selected, so why you use “false”?