LVL 2 Artifacts missing two

[Serenity]

Besides the one that the large giant drops while your finding dynamite and one in that small chamber in the hall way after the first machine gunner where you hit numerous switches to open that little room that hurts you while your inside it for some odd reason. I cannot simply find or even see the 3/4 artifacts, if you play the level over again it will allow you to gain another artifact from the giant but will expire after the level is over so two more are still needed to be found somewhere and i have explored nearly every square inch of the level and cannot seem to find any secret location/switches to find these last two.