I have a K&N "Aircharger" on my SUV, a 4x4 Nissan Armada. They call it a CAI, but it's really just an slightly longer SRI with a three sided metal box. The forth side is open to a factory hole in the left wheel well. The top is open but has a rubber gasket that seals with the hood. You all know the K&N design.
That thing is LOUD. Oh, did I say it is loud? Just in case I forgot to mention it, it is loud as hell when the 5.6 Nissan V-8 opens up. My wife would not ride with me in the SUV and she does not even notice the MSCAI on the Mazda.
I ended up putting soundproofing material, Dynamat on all sides of the metal shielding, and on the hood over the filter. It reduced the noise some, to the point that my wife will ride in the SUV, but it is still quite bothersome to her.
The MSCAI in short ram mode is similar in extra noise, but not nearly as bad, IMHO.