So I had all four wheels re-balanced, and also had a four wheel alignment. I am still getting this vibration at high speeds. Below 60mph it is OK, but between 60 and 80 it is very bad. Once I go above 90mph it seems to go away. What could this be? I thought for sure it was a wheel balance or alignment, now I have NO IDEA. Please HELP! PS..It's a 99 A6 2.8 with 104,000 miles.