I've had my Acadia since the end of February. From the day we took delivery there has been a vibration that begins at about 53MPH. It is most noticeable when you rest your hand on the console, but can be felt through the seat and steering wheel. It does not change in different gears or even when coasting until the speed drops below about 53 MPH, then the vibration goes away. I did not get a chance to take it back to the dealer until last week. They balanced all the wheels and then did a road force balance and said the right rear tire/wheel was the problem. They took the tire off the rim, reseated it and said it was fixed. It was not. I took it back on Tuesday and they are still working on it. They have ruled out the tires/wheels and apparently have GMC engineering involved in trying to figure it out. Anyone experience this type of problem?