"A lot of exhausts now have a small (2 or 3 mm) hole drilled at the bottom back edge of the silencer to allow water to drain."
If it's an understood beneficial feature, Do Audi utilize this feature in all their vehicles? I suspect a pinhole could exacerbate noise and corrosion issues if not properly designed?
Modern design is about understanding utility, I highly doubt Audi would purposely design exhausts to rust from the inside(they almost certainly have the cream of the best global designers/techs). I also doubt if ALL A3's show the same behavior The level of emission vapor is relative to many factors. The challenge is to get a statement from Audi on what is 'Normal'.
if you feel your vapor emissions are excessive you should address this with Audi IMO, it's not an easy ride, but I feel too many people just take it as accepted for ease of life, if there is an issue and it's addressed, it benefits all. Stand on the street for 10 minutes in morning traffic and get a feel for 'the norm' observing passing traffic. I really think there is an 'issue' with 'some' vehicles and it's being ignored. This time of year is a really good time to get a handle if there is an issue as any symptoms are clearly visible!
Better still, take a camera into a dealership and film the vehicle movements for 30 mins on a cold morning, if your vehicle is outside the 'norm' it gives you something to think about.
on the other hand, life is relatively short, 30 mins on a forecourt vs 30 mins of pleasure is a tough measure.
just steaming off....