I purchased the 2007 Mustang GT last September from a private seller. He disclosed (and it was obvious) that his aunt who was the owner drove the car into a ditch. The alignment was way off but still driveable. I took the car to Firestone and they aligned it and gave me a fancy printout. Ever since the car has pulled just a little to the left, but then for no reason it will track straight as an arrow at 70 mph. Then again for no reason it will start pulling lightly to the left. Any ideas what is going on?