Could be rail dust.
Is it on plastic bits as well like the bumpers?
Not sure if this is 100% correct but it is food for thought
From the web
A question was recently presented to me by a reader regarding “rail dust.”
First of all, “rail dust” if removed properly does not come back.
Rail dust is exactly that, when cars are transported by train (rail) from the factory to a city, the metal wheels of the train cars running on metal rails create small particles of metal that fly into the air and land on the horizontal surfaces of the car.
They are hot and will adhere to the paint. Then when they get wet from rain; snow or just dew they rust and create tiny little rust spots which are quite visible on white, yellow, beige or light colored cars.
The proper way to remove them is to soak towels in “rail dust remover” and lay the towels on the offended areas of the vehicle. Follow the manufacturer’s recommended dwell time to allow the chemical to dissolve the rust spots and loosen the particles of metal.
When this is accomplished rinse off the car with high pressure water to insure all particles are gone.
Then pre-spray the car with a mild alkaline cleaner to neutralize the acidic rail dust remover. If you do not do this, acid will remain on the paint finish and when it gets wet it will be active and could etch into the finish.
Then rinse off the alkaline chemical and follow that with a thorough hand car wash using a mild carwash shampoo and water.
To be safe, a coat of wax or paint sealant should be applied to the paint for protection.
Never use clay to remove rail dust because all that does is break off the tip of the metal particle, leaving a part of the metal still on/in the paint and when it rusts the spots will come back. If a paint finish offended with rail dust is properly treated chemically, then that should solve the problem.
You certainly do not want to repaint a vehicle unless you are absolutely certain there is no rail dust residue on the car. Of course, a competent paint shop would insure this to be the case before repainting.
If a detail shop, auto dealer or body shop attempted to remove the rail dust and it comes back, it is a good assumption that they do not know know what they are doing, or implemented the incorrect process.
rail rust
Beth
November 13, 2012
I have been reading MANY definitions of rail dust online. Several have said that rail dust is NOT only produced by trains. It's also been said it can be produced by exposure to anything from sandblasting to acid rain, from your disk brakes, or even from industrial areas. I have a 2010 white Challenger that has rail dust all over but is very fine and hard to see. My car was not transported by rail as it was made in Brampton, Ontario. Chrysler has been informed of this. The took pictures and sent it to Chrysler Canada to see if they would cover it under warranty. Do you know if this is usually something covered by warranty? Thx, Beth
detailer
Tom
March 26, 2013
No Beth, I don't think it will be covered by warranty, because its not the fault of the manufacture. I've been in the detailing business for 25 years,I deal with rail dust almost daily. It comes from driving on wet roads contaminated with these metal particals. I use a product called rail dust remover, its an acid based cleaner. I spay it on the vehicle after I've washed it and leave it on for about 20 minutes to a half hour and then just re-wash the vehicle. It all come off. Then the vehicle should be waxed after.
