I would peek under the hood and make sure all the coupler hoses in the intake (from the airbox to the turbo) are intact. If one of them was left off, it makes that sound, and means you are not pulling air through the air cleaner. The hoses are secured with hose clamps, and there's a good chance some of the stuff under the hood was removed during the RV build, and sometimes things get missed during the re-install. The 6.7L normally does not make much intake noise, and the fan should only engage during idling and hard pulls on hot days.
