I had problem with my q7 i from Canada very cold park my audi in garage over night in the morning cant start i spend 2 days to find what was wrong ,car start and after 5 sec die my exhaust system was complete frozen i heating muffler and pipe ,drill 2 small holes 1/8" at lower point of muffler and the car start no problems in my garage was -temp -10 water was coming from the system

 

I have seen this happen more than once. I recommend anyone living in cold climates (like here in Wisconsin) drill a small hole in each end of the muffler at it's lowest point to allow the condensation and normal water produced from the combustion process. Most vehicles have the small weep holes from the factory, Audi doesn't seem to all the time.

Also, the higher the ethanol percentage in the fuel, the more water you'll get out the exhaust.