Problem with Space Shooter Tutorial

Hey guys,
I have been going through the tutorial and so far have only come across two problems I couldn't find the solution to elsewhere

1. The player explosion sound refuses to play when it collides with an asteroid, it only plays the asteroid sound but the particle effect goes off.

2. the scrolling background jumps to 0 on the y covering the scrolling stars and then gets pushed out on the z so that it scrolls back onto the main scene which is just white
this is the background scroller script if this is a script issue

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class BG_Scroller : MonoBehaviour
6. {
7.  
8.     public float scrollSpeed;
9.     public float tileSizedZ;
10.  
11.     private Vector3 startPosition;
12.  
13.     // Use this for initialization
14.     void Start () {
15.        
16.     }
17.    
18.     // Update is called once per frame
19.     void Update ()
20.     {
21.         float NewPosition = Mathf.Repeat (Time.time * scrollSpeed,tileSizedZ);
22.         transform.position = startPosition + Vector3.forward * NewPosition;
23.     }
24. }
25.  

thanks in advance.