[olrocker]

The dealership should (if it’s under warranty) and a good shop will, put it on a lift then get in and simulate the driving characteristics you’re describing on the lift. One guy will get in, Start the car, get it up to 75 mph, and another guy stands under the car. Then the guy inside will lift off the throttle while the other looks and listens in all the areas of the rear end and drive train. They can look and listen closely to everything from the driveshaft u-bolts to the whole rear end and keep repeating till they find it.