Hey, thanks for your reply. I should however, have mentioned that you can only really hear the hissing over the sound of the engine when you lean all the way in over the head cover and put your ear near the throttle body. If it makes more sense now let me know. But regardless, if there's a leak, I have to take the manifold off anyway in order to check for and fix it. I haven't gotten the time or the nerve to perform this surgury yet, but time time is drawing near. Anyway, it's still a myster and any more help anyone can offer would be greatly appreciate.