I have a 2018 Prestige A7 with Nardo Grey paint.  I take great care of my car, however, out of the blue just noticed about a 12" section under the spoiler where the paint has just peeled off.  Has anyone else experienced anything like this?

Did you buy the car new or from Audi approved? How long have you had it? Abd I'm taking the spoiler is standard. I ask these questions because paint warranty will only be valid if the paint is original. 

Ive had the car for 2 years.   Yes was certified,  under warranty and all paint and spoiler original.  Anything I should know?  Or just call my dealer?

I'd definitely get it to a dealer as it shouldn't have done that. But be prepared for be a fight on your hands.