Ok so i have an 2002 Audi A4 1.8T with aftermarket wheels. I bought the car and the only vibration it had was in the front at pretty high speeds and even then it wasn't bad. So i decided to put new tires on it. I went to the local tire place. Shortly after I noticed a highway vibration that was driving me insane. It felt like it was coming from directly below my seat. But I also could see my passenger seat moving from the vibration as well. Suspect I returned to the tire place to have it balanced again. That didn't help in the least. I took it to two other places and had it balanced. Didn't help. THen i purchased the hubcentric rings. This helped but its still there. I also had a mechanic replace a front half shaft thinking that was causing the vibration. Well it wasn't. So i finally broke down and took it to audi. Audi looked at and in five minutes said out of round tire. I immediately called the tire place and explained the situation and they gave me a free set of tires ( different brand-KUMO's). The vibration was again better but was still there. I had it balanced several more times and even took it back to audi and they couldn't find anything wrong. They said they checked every joint known to man in that car and everyone of them looked good. The even told me that the rims looked perfect as far as not being bent or anything like that. Does anyone have any suggestions out there.