Unity Volume Slider dont works correctly,need help!

Hi,i have made volume slider script (C#) for my Main Menu,but volume slider dont works!
Slider have values from 100 to 0,only when i get to 0 then sound just mutes,but when its up to 0+++ no any reaction sound jus stays in default volume set,please help! II posted a short line of script,i hope you can help me,with my problem.

Script line:

void AudioOption()
	{
	
		//Music
		GUI.Label(new Rect(Screen.width / 2 - 175,165,300,70),"Music: ");
		skin.label.alignment = TextAnchor.MiddleLeft;
		GUI.Label(new Rect(Screen.width / 2 + 25,165,300,70),musicValue.ToString());
		skin.label.alignment = TextAnchor.MiddleCenter;
		musicValue = GUI.HorizontalSlider(new Rect(Screen.width / 2 - 100, 217, 200, 30), (int)musicValue, 0, 100);
		audio.volume = musicValue;

I hope you understand me,please help me!