So my truck has 14k miles on it and it was making a howling noise between 20 and 40 mph. Sounded like gear howl. The Nissan dealer replaced the carrier bearing on the driveshaft yesterday (apparently there is a bulletin on this). The howl is gone. Now however when I hit 70 mph, there is a vibration and you can hear it as well as feel it. It's not major, but it definitely was not there before. Any ideas before I take it back to the rocket scientists in the service dept.?