Scale gui button to resolution and playing audio

Hi I have a pause button that when pressed sets time to 0.

When it is at 0 I draw 2 buttons onto the screen, a resume and menu button.

I have two problems; when I click resumethe sound plays fine, when I click menu the sound cuts out too early, how can I fix this ? a tutor mentioned something about invoke.

Also another problem I have is scaling these two gui buttons to the screen resolution, how can I go about adapting code so the buttons scale with resolution ? thank you in advance.

my code is

 using UnityEngine;
 using System.Collections;
 
 
 public class pauseScript : MonoBehaviour
 {
 
     bool Pause = false;
     public GUIStyle ResumeStyle;
     public GUIStyle MenuStyle;
 
     void OnMouseUp()  {
         {
             audio.Play();
 
             if (Time.timeScale == 1)
             {
 
                 Time.timeScale = 0;
 
 
             }
             else
             {
                 Time.timeScale = 1;
             }
         }
     }
     void OnGUI ()
     {
 
 
         if (Time.timeScale == 0)
         {
             if (GUI.Button (new Rect (Screen.width/2-50, Screen.height/2-25, 100, 50),"",ResumeStyle))
             {
                 audio.Play();
                 Time.timeScale = 1;
             }
 
 
 
             if (GUI.Button (new Rect (Screen.width/2-50, (Screen.height/2-25)+60, 100, 50),"",MenuStyle))
             {
 
 
                 audio.Play();
                 Time.timeScale = 1;
                 Application.LoadLevel ("MAINMENU");
             }
         }
     }
     
 }