I recently installed a K&N air intake on my 05 f150/w 5.4 and noticed a hissing sound under the hood during acceleration. I think it's just the intake sucking air, but wanted to see if anybody has came across this or what your thoughts my be.

 

Its just the filter working..it should sound like that so its ok. nothing to worry about just enjoy it

 

Ahhhh... the sound of dirt sliding through the intake pipe.....