What happened? While driving at highway speeds (approximately 60-75 mph), the vehicle exhibits a pronounced up-and-down motion at the rear, commonly referred to as aœporpoising.a This motion is especially noticeable when traversing uneven road surfaces or expansion joints. This issue compromises vehicle stability and passenger comfort, posing a potential safety risk during high-speed travel. The problem has been consistently reproducible under similar driving conditions. The vehicle has not yet been inspected by a dealer or independent service center for this specific issue. No warning lights or error messages have appeared on the dashboard in relation to this problem. Component suspected: Rear suspension system (exact cause UNKNOWN). I am willing to have the vehicle inspected upon request.