I have owned my Solstice for around 3 months now. This has been happening ever since I bought the car. Under moderate throttle, I have a side to side swaying motion in the rear of the car. It's nothing so severe that it would make me lose control, but it is slightly uncomfortable. It doesn't happen under light throttle or even under full throttle. The rear is not breaking traction when it occurs. Is this normal or is this something I need to look at?