Well, since my Elite CC was also making this noise on my LLT, I decided to take the fittings off and put new telflon tape on it just to be sure no leak. As I removed the top fitting, I looked inside and noticed in the filter chamber they use some sort of "Scotchbrite" looking material on top of the filter element, that's when I realized that was the cause of the "hissing" noise!
If you take a piece of paper and blow on the edge you hear that sound, now multiply that a couple of times and you get the "hissing" noise.
I trully believe the rush of air into that chamber creates that effect. Also, the sound might be more pronounced if you have Ice-olator, plenum spacer, or Ported TB installed.