WARNING: This page is about a different car, the 2018 Audi A6 Quattro, 2017 Audi A6 Quattro, and 2016 Audi A6 Quattro. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Front final Drive Cover Tightening Sequence
Courtesy of AUDI OF AMERICA, LLC
-- Tighten the bolts in two steps in the sequence shown.