I purchased my new Weber Q 1200 a few months ago and I noticed the grates started getting a light brown coloring on them….rust.  My grill is always covered outside and it hasn't rained here in a very long time.  I use a soft wired brush to clean the grates, as approved by Weber and I never use a metal scraper.  The porcelain enamel coating is supposed to be thicker than the previous versions.  I contacted Weber and they are going to send me out new grates, but I still have to wonder why they are getting rust in the first place.  It's very disappointing.