This might be a stupid question, but are you sure that your tow and camber are set up correctly. When I got my gensis out of the box and ran it for the first time it did the same thing. I looked at the wheels and I could see that the tow was off. I aligned everything, and it was fine from there. Check the amount of play in your wheels. You may have to shim them to get rid of the play.
Good luck..