Strong Vibration 1.8lt A-4 2004 multitronic

Hi!! My 1.8lt A-4 2004 model has a strong vibration when at drive position, reverse, and when accelerating at around 70-80km/hr and even higher speed at 100-140km/hr. Its only when accelerating or being at a stop light (if open, the window starts shaking) or maneuvering to park the car. Could it be the engine? I dont think its the suspension since the vibration stops when in neutral and when at a vibrating speed (70-80, or 100-140km) you stop accelerating, the suspension feels just fine. It feels like if my tires were full of bumps and theyre completely new!! It gets worse when the A/C is on. I already changed the 3 motor supports/mounts in the Audi Service and it doesnt help. Could it be the muffler eventhough its seems firmly set? Please help me!!