Tapping noises, Audi A3 8P rear hatch/trunk lid (Solution)

In the Audi A3 8P, the upper mounting screws that secure the lower plastic interior trim of the tailgate can become loose. These screws then fall down into the tailgate.
When the tailgate is closed or when driving on rough roads, it rattles because the screws in the tailgate are loose and bouncing around.

Two retaining screws are located in the recessed area of the aforementioned cover. Two additional retaining screws are located on top, underneath the removable covers of the cover.
At the remaining attachment points, the trim is only clipped onto the metal of the tailgate.

You can use slightly larger screws or modified mounting brackets, or simply reattach the screws with a dab of body sealant to prevent them from coming loose on their own.