Rename variables fix some behaviour

Assets/SoundManager.cs

-using UnityEngine;
+using UnityEngine;
 using UnityEngine.Events;
 using System.Collections;
 using System;
 
+[RequireComponent(typeof(AudioSource))]
+[RequireComponent(typeof(Collider))]
 public class SoundManager : MonoBehaviour
 {
-    public Boolean stop_on_exit = false;
-    public Boolean pause_on_exit = false;
-    public Boolean start_on_enter = true;
-    public Boolean start_after_awake = false;
-    public Boolean play_only_once = false;
-    public float start_delay = 0.0f;
-    public float stop_delay = 0.0f;
+    public Boolean stopOnExit = false;
+    public Boolean pauseOnExit = false;
+    public Boolean startOnEnter = true;
+    public Boolean startAfterAwake = false;
+    public Boolean playOnlyOnce = false;
+    public float startDelay = 0.0f;
+    public float stopDelay = 0.0f;
 
     Boolean never_played_before = true;
     AudioSource source;
@@ -19,40 +21,42 @@ public class SoundManager : MonoBehaviour
     void Awake()
     {
         source = GetComponent<AudioSource>();
-        if (start_after_awake)
+        source.playOnAwake = false;
+        source.Stop();
+        if (startAfterAwake)
         {
-            Invoke("Play", start_delay);
+            Invoke("Play", startDelay);
         }
     }
 
     void OnTriggerEnter(Collider other)
     {
-        if (start_on_enter)
+        if (startOnEnter)
         {
             // Start sound only if we want to "restart on enter"
             // Otherwise only start it, if it isn't playing already
             if (never_played_before || !source.isPlaying) 
             {
-                Invoke("Play", start_delay);
+                Invoke("Play", startDelay);
             }
         }
     }
 
     void OnTriggerExit(Collider other)
     {
-        if (stop_on_exit)
+        if (stopOnExit)
         {
-            Invoke("Stop", stop_delay);
+            Invoke("Stop", stopDelay);
         }
-        else if (pause_on_exit)
+        else if (pauseOnExit)
         {
-            Invoke("Pause", stop_delay);
+            Invoke("Pause", stopDelay);
         }
     }
 
     void Play()
     {
-        if (play_only_once) {
+        if (playOnlyOnce) {
             if (!Data.instance.PlayedSound(source.name)) {
                 source.Play();
                 never_played_before = false;
@@ -61,6 +65,8 @@ public class SoundManager : MonoBehaviour
         }else{
             source.Play();
             never_played_before = false;
+            Debug.LogFormat("Registered as Played: {0}", source.name);
+            Data.instance.RegisterSound(source.name);
         }
     }