This is almost always the result of bad starter box aligment. You need to move the wheel over
(Not all boxes allow for this) so the highest point is in the chassis. What happens is the high
side of the wheel hits first and to allow the wheel more travel they gring on the chassis.
Not always the case actually. Some bump box wheels are simply too big to actually fit into the cut out. Which is why i had to change starter boxes as the one i originally bought, the wheel was too big to fit into the cut out.