Hello, I bought an Audi A6/ Avant / C4 / 2,8l / Quattro 2 days ago. Runs up to 120 kmH like a Swiss clockwork. Then I wanted to know what 193 hp could do….. I accelerated up to the highway and at approx. 140 kmH hit-like vibration in the steering wheel, on the front axle and the whole body. I thought, I ride over cobblestones with 140 things and breaks apart the whole car. I almost got into my pants in front of a shock. I don’t know what the vibration caused. I am on the highway right on the brake and under 120 kmh the phenomenon was gone again. What could have caused it?