wiggle of the starting line.

Also it could be the alignment. As the wheel drops down on the launch the toe changes. The tie rods effectively gets shorter which toes the front tires out. Then whichever tire grips better or hits a seam or any number of reasons, that tire steers the car. Then it can change to the other tire and back and forth. With it jacked up measure toe with a tape measure. Tire groove to the corresponding other tire groove. Do it in front of tire and back. How much different