Could be tire imbalance. If the vibration does not seem to affect the steering, it's probably one of the rear wheels.

Have your car's underbody washed and see if it still shows up. Sometimes, dried mud can cause rotational imbalance on the wheels.

Your vehicle is still relatively new, so it's probably not a worn U-joint or an unbalanced propeller shaft.

An extreme angle to the U-joints will also cause vibration, but this usually starts to happen at lower speeds. Just in case, make sure the vehicle did not undergo any major modifications to the ride height, which may cause uncorrected angles in the driveshaft.