I have a 2006 A3 1.8T 6 speed. At about 40 mph it starts vibrating and which seems like it is coming from the rear and I can feel it under the drivers seat. This gets pretty bad through about 65 mph. At about 70 mph the vibration stops and it gets very noisy - almost like your driving over rough road. Does anyone have any idea what is going on? This started after the tires were inadvertently inflated to 44 psi (recommended is 28 psi for A3). They are all now back to 28 but the vibration/noise hasn't stopped. Any ideas? Should I get it off the road?