Sounds like what they call rail dust ( iron oxide particles from trains also the sand on roads in the winter), you get them here in winter from the roads. Clay bar them or a good cleaner wax.
Thanks for the heads up and the info, I have lived in the same area for a long time and never had this on any of my other vehicles but what you say makes sense. I pass under elevated trains all the time.Sounds like what they call rail dust ( iron oxide particles from trains also the sand on roads in the winter), you get them here in winter from the roads. Clay bar them or a good cleaner wax.