I do recall in my Buick days that the rotors on some GM cars had to be turned when new! The Factory surface on new rotors was supposedly inadequate for proper ABS performance. We took just enough off to apply a non-directional surface. The non-directional finish removes the spiral effect of turning the rotor, which in turn keeps the pads from moving up and down in the caliper. Anyway, the point I'm making is they may have accounted for this by producing the rotors slightly oversized. If and when you replace your front rotors again tell the shop you want them turned with a non-directional surface. If they don't know what you’re talking about, it would be best to take them to a GM dealer and have them done.