K&N
I have the K&N CAI on a 08 5.4L it doesn't make any noise until about 3000 RPM. It doesn't make any noise at idle or cruise. I remember my past CAI on my ranger with the 4.0L it would howl at idle, and it seems the humidity (weather) had an affect on just how bad it growled and yes it does get irritating after a while. But if you looking for the "hot rod" sound, the K&N does without any problems and is supposed to add 15HP and some tourque too. I'm happy with it.
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