I'm not convinced those balls do anything, certainly not enough to make the knocks you guys are hearing.
BTW I took a test drive today in a Cooper (standard sports suspension) and I'm sure I heard it knock when I slowed down
My wife doesn't hear these noises and I'm trying to train myself not to hear them also. I tell myself that the car is absolutely brilliant so forget it.
Scotty - try lowering your rear seats as well. If the noise is different then the rear seat catches may need adjusted also.
Good luck but most of all enjoy your car
