While driving in cruise control between 35 to 40 mph, going up a small incline, the engine bogs down and the vehicle rattles. i have had the vehicle checked out 5 times by different dealers and their conclusion was that this is a normal condition. the transmission shifts into the highest gear for fuel economy. i do not believe buick would make a vehicle that rattles at 35 to 40 mph. going into manual 5th gear stops the rattling, but that should not be the solution.