I changed my Yokohama's for Pirelli P Zeros (same car - Audi A7 SLine BiTDI) and am very happy with them. I have done over 20000 miles with the back set, and think I will get about 5000 more, so 25000 miles for a tyre is pretty good (I don't exactly drive slow!).
As for noise, I think the size of the wheel has more to do with it than the tyre. I don't really notice any noise, but then again, I pretty much always drive with music.