How to make audio play at once.

Questions & Answers
1

My background music starts playing when you get into the main menu. But if I go to another scene and come back to the main menu the background music starts playing one more time. So they are playing on top of each other its like I hear the music from two different sources and they are not synced.
My script:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Animations;

public class MusicClass : MonoBehaviour
{

    AudioSource bgSource;

    void Start()
    {
        bgSource = GetComponent<AudioSource>();
        bgSource.Stop();
        bgSource.Play();
    }


    void Awake()
    {
        DontDestroyOnLoad(gameObject);
    }
}
2

public class MusicClass : MonoBehaviour
{
private static MusicClass instance;
private AudioSource bgSource;

     void Start()
     {
         bgSource = GetComponent<AudioSource>();
         bgSource.Stop();
         bgSource.Play();
     }
 
 
     void Awake()
     {
         if(instance == null)
         {
             instance = this;
             DontDestroyOnLoad(gameObject);
         }
         else if(instance != this)
              Destroy(gameObject);
     }
 }