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Here's Audis take on the D4 4.0T Tfsi Active Engine Mounts :

Active engine mounts: counteracting vibration for greater refinement
Audi normally uses firm, sporty settings for its engine mounts. For many years now certain models – notably the A8 at the top end of the range – and various engines have had switchable electromagnetic mounts. These have two operating settings: at idle speed they have a “soft” characteristic to prevent noise and vibration from reaching the interior, but when the car is being driven a firmer damping rate is selected in order to suppress engine vibration.

The active engine mounting that Audi has developed for the 4.0 TFSI takes this technology a decisive step further – it cancels out engine vibrations with out-of-phase counter-oscillations. The key component is an electromagnetic oscillating-coil actuator. This has a rapid stroke that is transmitted via a flexible diaphragm to the hydraulic fluid in the mounting, which also absorbs oscillating movements from the engine. In the fluid these are overlaid by the actuator movements and cancelled out.

The control units for the active engine mounts receive their signals from two sources. Engine speed is detected by the crankshaft sensor; these signals are used to compute the precise phase and frequency of the actuator signal. Acceleration sensors on the two engine mounts supply the data that determine the amplitude necessary to cancel out the vibration.

When the new 4.0 TFSI is running in the four-cylinder mode, it generates a certain amount of engine vibration and drumming noise of what is known as the second order. They are not typical of a V8, but the counter-vibration generated by the active mounts reduces them to an undetectable level.

At idle speed with all eight cylinders in operation, engine excitation of the fourth order occurs. This too is largely eliminated by the active engine mounts so that the engine appears to be running even more smoothly.