I know in my case it was not rust, but appears to be some sort of residue from something during manufacturing. Anyway it came off very nice with some polish. Did not try anything like Windex or even water so don't know. Mine looked just like "fourdoor" only that car had a little more of it. Hope fourdoor posts today to let us know what the dealer thinks. It does not look like pitted rust where it would come from under the paint and push outwards so I think its just a stain.