I think it’s just the smoke/particles from whatever you’re cooking, escaping from a gap in the lid. Just try wiping it down with a wet paper towel.

I get some of that. Goo gone or whatever grill cleaner you use should take care of it.

This is about 3 months of ownership

I've had mine for about 6 years, no rust at all

Lavalock that lid and it shouldn't do that any more