Hi all! I've owned my 2007 Cooper S for 9 years with very few problems, but recently I notice a catch or notch in the steering while traveling at moderate speeds (40 to 70 mph). It is only present at top dead center and can be best felt by simply moving the wheel slightly left and right at cruising speed. My mechanic has looked at it on 3 occasions, but no resolution. Any ideas would be appreciated. Thank you!