[Koala Yummies]

I think you just need to clay-bar the surface, and seal it with some good wax. It's usually just some contaminant, brake dust, rail dust, small corrosive particles that are the result of vehicle and road wear.

 

[Koala Yummies]

Here are some good diagrams that illustrate what the little rust spots are and what they do, how they're stuck etc. (for those who haven't seen these)

Wolfgang Elastic Poly Clay Bar, wolfgang car care,wolfgang clay lubricant,clay lube,clean water spots,remove water spots from car,compound car,clay

Clay Bars | What Clay Bars are and how they work

Detailing Clay Bar and Lubricant

http://www.acmenovelties.net/cars/images/paint_wax.png