2005 Jeep Cherokee powertrain problem

I have an 05 Jeep GC-RWD. A continuous loud humming noise (like having a subwoofer on in the back) starts at 60 mph and goes away at 65 to 70 mph. Everything's fine once passed 70 mph. Feels like it's coming from somewhere between middle and the rear. Possibly amplifies and resonates inside the car. Occurs both during acceleration from 60 to 70 and deceleration from 70 to 60. Gone once droped below 60 mph. I feel slight shaking. Obviously rpm/speed related. Dealer replaced the ring and pinion gears on the last day of warranty. No change what so ever. Appreciate your comments.