A faulty transmission can cause vibration for a number of reasons. First, if the transmission is not properly secured to the engine, it can cause vibration. Second, if the transmission fluid is low or dirty, it can cause the gears to grind and create vibration. Third, if the torque converter is not working properly, it can also cause vibration. Fourth, if the clutch is slipping or not engaging properly, it can also cause vibration. Finally, if there are any worn or damaged parts in the transmission, they can also contribute to vibration.