This is the script for the zombie. For this section, I've cut out most of the script to only include the audio portions.

Enemy_Zombie.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Enemy_Zombie : Entity_Parent {

	  //We create reference to the AudioSource that we can drag in because the zombies are a prefab
    public AudioSource Source;
    //This is the Audioclip of the zombie dying. Audio clips are made by downloading sounds from the internet and dragging them into the asset window
    public AudioClip DieClip;
    //This is the clip for a zombie snarling. It plays periodically.
    public AudioClip SnarlClip;
    //This is the time between the zombies snarling
    public float AudioInterval;


        
	void Start () {
     
        StartCoroutine(PlayGrowl());
	}
	
	// Update is called once per frame
	void Update () {
        
        CheckAttack();      

        if(current_Health_Level <= 0)
        {
            //PlayOneShot is a command from the AudioSource Component which lets us play any audio clip we feed into the function
            Source.PlayOneShot(DieClip);
            Die();
        }
       
    }
    
    //Here we define a coroutine that will use PlayOneShot to play the snarlclips every AudioInterval seconds with an addtional random range
    IEnumerator PlayGrowl(){
        for(;;){
            Source.PlayOneShot(SnarlClip);
            yield return new WaitForSeconds(AudioInterval + Random.Range(0, 10.0f));
        }
    }
     
}