strongly recommend you flush, with hyd fluid your hyd system, with front on jacks and cycle steering stop to stop, drain/empty and repeat. Hyd system needs clean non contam fluid or it will mes everything up which gets $$$$$$. The steering rack is very prone to dirty contam fluid. Man reccommends every 2 years do it yearly. Every Audi I have owned 1978 Fox, 87 TQ5K, 95 100, 2001 2.7T have done this with. Always drained and replaced hyd fluid racks and barkes lasted over 250K on each. expect 2.7 only 70K so far.

Advise you get a VAG COM hook up your lap top and check the faults and O2 sensors, we have 6 at aver $100 each this gets pricey. VAGCOM and fault codes make doit yourself repairs MUCHO easier. remember our cars run on computer and sensor inputs these sensors are important and get effected bad connections and exhaust contaminates. I doubt it is your surge valves your turbos do not work much at start up. But stock valves are cheap check eBay. The way your treatin this now you will do more damage on start up by reving a cold engine. It will last longer like our body parts if it is warmed up first. Good luck

 

Did you have the front-end checked...MY2000 A6 2.7T needs outer tie-rods @ 54k. That might be your noise.

 

Funny thing, i brought my car into the shop yesterday for these same 2 items, as well as a few others. The guy aty the desk asked what kind of gas i use, since i use 93, he said in colder weather use reg, or a lower premium, nonetheless they are checking it out. I should recieve word by noon and i will update this post then..

 

yea could be tie rods. put ur car in park, start jerking the wheel left to right left to right and see if it clunks

 

Golt my car back, they said it was a loose shield or guard, the sputter they said is from the higher oct in the cold, checked it out fully, they said, well at least i have it on record.