My 260E did the same thing and it took two pair of Goodyears, a set a BF Goodrich before it stopped with a set of Michelins. Mine wouldn't start the subtle vibration until 65 mph, so I thought maybe it was mechanical and off to my mechanic I went. He showed me where the tires were out of round, and these were new. That is when I got my Michelin tire speech. Mounted the Michelins, and it hasn't vibrated since, at any mph.