How do I aim to prevent the OB from rattling out of a corner pocket?
This happens when the ball hits the near rail cushion or point with speed before entering the pocket. Here’s a good demonstration of this effect:
Also, super slow motion clip HSV 3.8 shows why it happens fairly clearly. The cushion imparts sidespin to the ball, changing the rebound angle off the inner wall of the pocket. The following instructional articles also have some good illustrations, descriptions, and online demos of this and other related effects: