I had the same problem about drifting from day 1. It's not THAT bad, but definitely noticeable, and as yours, my car drives straight and true otherwise. All these comments about tires and alignment are off the mark. They're not seeing the question!!!
I suppose I'll just live with it, as you probably will. This topic has come up before many times on other forums as well, and the usual reply is -- that's just the way it is! And again, it's not THAT bad.