I had a 17 in. set of Toyo tires put on and had same thing happen. Dealer put tires on one of there machines and showed me that 3 out of the four tires were not round ( I was supprised too) Replaced them with Michelins and problem was gone. Dealer told me there is a differnce in tire quality and that these cars can tell.

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98 E430(sport), 99 ML 320 (sold) , 05 C 230(sport) Mark