IHAVE A VIBRATION THAT STARTS AT ABOUT 40 MILES.

IHAVE A VIBRATION THAT STARTS AT ABOUT 40 MILES PER HOUR AND UP, I put on new tires, tryed a different set of tires and whells, had wheel alignment and balance, checked drive shaft run out. Replaced front ball joints, had to dealer and they could not find problem, they suggested this is normal. I disagree, any one have any suggestions.