mine does the same,
push the car harder in the corners and it goes away.
can only think that the sport with harder suspention than gs 300 is the cause
my last car 325 bmw was the same,
first got mine in february, it was like that when i bought it , i then put 275x35x18`s on the back
and still the same.
i have really hammered mine on some corners and the road holding is unbelievable for such a large car.
will go round corners a lot better at speed than the 325, which i also uprated from the standard springs.
i would say don`t worry