ok yes I do have two different sets of tires. I had switched them in the past to see if it was the wheels and at the time the vibration was still their. Since then I haven't not checked again. I am going to try switch the aftermarket ones with the originals one again to see if it feels any different. Also I did swap them front to back and the vibration did not change any. I'm still wondering if it has something to do with the hubcentric rings not being exactly right in the back. This car I swear

 

are you having any loss of power?? if so its probably not the drivetrain at all. just a coil. i had a coil go out on my 2003 1.8T twice. when that happens the motor only runs on 3 cyls. therefor throwing the balance of the motor off and thus a severe vibration occurs...i had a sever power loss....to the point of not even getting up to 60+MPH. coils are really cheap. my local audi mechanic charged me about $175 for the coil and instal. i hope this helps...