Beginner script problem

Solution 1 : Sound will play continuously while you're closer to the target then 5.0f

 using UnityEngine;
 
 public class asd2 : MonoBehaviour
 {
 
     AudioSource _audio;                                                 //renamed it to _audio
     float distance;
     public Transform A;
     public Transform B;
     public AudioClip impact3;                                           //Assign this in Inspector or Initialize it in Start() / Awake()
 
     void Start()
     {
         _audio = GetComponent<AudioSource>();
         //A = gameObject.CompareTag("Player");                          //CompareTag returns bool
         //B = gameObject.CompareTag("ghost");                           
         A = GameObject.FindGameObjectWithTag("Player").transform;       //FindGameObjectWithTag returns GameObject
         B = GameObject.FindGameObjectWithTag("ghost").transform;
     }
 
     void Update()
     {
         distance = Vector3.Distance(A.position, B.position);            //removed float as it is declared above
         if (distance <= 5.0f && !_audio.isPlaying)  
         {
             _audio.PlayOneShot(impact3, 0.7f);
         }
     }
 }

Solution 2 : Sound will Play once

 using UnityEngine;
 
 public class asd2 : MonoBehaviour
 {
 
     AudioSource _audio;                                                 //renamed it to _audio
     float distance;
     public Transform A;
     public Transform B;
     public AudioClip impact3;                                           //Assign this in Inspector or Initialize it in Start() / Awake()
     public bool audioPlayedOnce = false;                                //Check if Audio has been played
 
     void Start()
     {
         _audio = GetComponent<AudioSource>();
         //A = gameObject.CompareTag("Player");                          //CompareTag returns bool
         //B = gameObject.CompareTag("ghost");                           
         A = GameObject.FindGameObjectWithTag("Player").transform;       //FindGameObjectWithTag returns GameObject
         B = GameObject.FindGameObjectWithTag("ghost").transform;
     }
 
     void Update()
     {
         distance = Vector3.Distance(A.position, B.position);            //removed float as it is declared above
         if (distance <= 5.0f && !_audio.isPlaying && !audioPlayedOnce)  
         {
             _audio.PlayOneShot(impact3, 0.7f);
             audioPlayedOnce = true;
         }
         else if(distance >= 5.0f)
         {
             audioPlayedOnce = false;
         }
     }
 }

Note: Sent from tablet so above code is not tested. I hope I didn't make any mistake :D Let me know if it doesn't work...