added mixxing hearTheWorld check

public/client.js

@@ -127,7 +127,7 @@ setInterval(function(){
 }, 1000);
 
 function playExternalSound(){
-    if(externalGrid){
+    if(externalGrid && $('#hearTheWorld').is(':checked')){
         for(var i = 0; i < 4; i++){
             for(var j = 0; j < 16; j++){
                 if(externalGrid[i][j] != 0){