I spent most of yesterday trying to fix my gold material. If you zoom in real close you can see it has some weird pattern to it. I had this same problem in Marmoset as well. Only the gold or any really shiny material. However I did discover that if I use tiff 16 bit it looks beautiful. Problem with that is sketchfab doesnt allow for tiff 16 bit. Is there some other way to get around this problem?