I just noticed that the teeth on my cassetes ( I got 4 bikes) are not the same. One bike has all the teeth nice and flat on the top, another has alot of teeth that look like shark fins, and the other two have almost a pattern where like five or six teeth are flat tops and then there will be a sharkie. The bike that has the most shark shaped teeth came like that when I bought it brand new, so is it an intentional design, or factory defect?