I've starting to wonder the same thing about mine. My mustang is white and even when I first got it I noticed a few brown specs randomly on the car. A few I repaired by sanding and a paint pen when I first bought it. Others since then I have removed with some elbow grease when washing and in some cases with a scratch remover compound. There are some spots now that I've had the car for a year that just won't come out. I originally thought these were being caused by the crape mertyl trees over my driveway but I cut them down months ago. I park in a garage at work so no other trees dripping sap anywhere. Then I noticed this last time washing that in the trunk well some larger brown spots forming more then likely from the water that build up in there. So I'm really starting to think it is rust starting and the car is only 1.5 years old.