c'mmon its not fun enable it for every player online ;)

L2_GameServer/java/com/l2jserver/gameserver/model/actor/L2Npc.java

@@ -1592,7 +1592,7 @@ public class L2Npc extends L2Character
 	@Override
 	public void sendInfo(L2PcInstance activeChar)
 	{
-		if (Config.CHECK_KNOWN)
+		if (Config.CHECK_KNOWN && activeChar.isGM())
 			activeChar.sendMessage("Added NPC: "+getName());
 
 		if (getRunSpeed() == 0)

L2_GameServer/java/com/l2jserver/gameserver/model/actor/instance/L2PcInstance.java

@@ -10036,6 +10036,8 @@ public final class L2PcInstance extends L2Playable
 
 	public void leaveOlympiadObserverMode()
     {
+		if (_olympiadGameId == -1)
+			return;
 		setTarget(null);
 		sendPacket(new ExOlympiadMode(0));
         teleToLocation(_obsX, _obsY, _obsZ, true);
@@ -10046,7 +10048,6 @@ public final class L2PcInstance extends L2Playable
 			setIsInvul(false);
 		if (getAI() != null)
             getAI().setIntention(CtrlIntention.AI_INTENTION_IDLE);
-
         Olympiad.removeSpectator(_olympiadGameId, this);
         _olympiadGameId = -1;
         _observerMode = false;

L2_GameServer/java/com/l2jserver/gameserver/model/actor/knownlist/PcKnownList.java

@@ -112,7 +112,7 @@ public class PcKnownList extends PlayableKnownList
 			// Send Server-Client Packet DeleteObject to the L2PcInstance
 			getActiveChar().sendPacket(new DeleteObject(object));
 
-		if (Config.CHECK_KNOWN && object instanceof L2Npc)
+		if (Config.CHECK_KNOWN && object instanceof L2Npc && getActiveChar().isGM())
 			getActiveChar().sendMessage("Removed NPC: "+((L2Npc)object).getName());
 
 		return true;