Mine also has a "spooling up" noise about 48ish MPH. The dealer said all the TSB's were done, so I assume mine starting a little later explains the higher speed noise. Like Jasmine said, at the higher speed it does drown out with the natural drivetrain noises pretty quickly, or just turn the traction control off, or shift into manual, or turn the auto 4X4 on, and it goes away also. I am at about 95K on the clock, so I would think it is not effecting longevity, just an annoying noise FCA missed during development.
The other annoying thing mine does is a 18MPH shake, which the dealer of course has no good explanation. They blame it on the same issue as the "spooling up" noise.....which I doubt.