One problem related to engine clicking and tapping noises has been reported for the 2015 Audi A8. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2015 Audi A8 based on all problems reported for the 2015 A8.
Car ran rough on the way home from picking up take out dinner - metallic, rapid popping sound coming from engine bay (faint with window up). Car died while slowing at a stop light and would not turn on - steering wheel also locked, power brakes failed. I was able to bring my car to a stop before striking a boulder using non-power brakes. Car was towed to nearest Audi dealership and I was informed that both (!) turbos failed at just over 70,000 miles and meticulous service. Oil was changed at half the recommended interval (@5,000 miles). Expensive repair that shouldn't be happening at such low mileage (and extremely frequently from owner reports) that also led to a completely loss of control and some brake function. Audi has a TSB on the issue, but wondering why the dot/NHTSA has yet to enforce a recall?.