Ok, so someone calls this "tramlining"
Other symptons that may or may not be related to this problem...
Mild vibration about 20 mph and goes away by 30.
sometimes a VERY HARD STEERING WHEEL SHAKING event at 45+ mph that is soooooo bad I have to pull over and slow down, then have another go at it until it goes away...
Again, this didn't seem to happen, or was hardly noticble with stock 15" and now the 18" BMW 2006 Wheels and Tires are wierding it....