A non-smoking question, hopefully you all know. I have a big box store propane grill that I've converted to natural gas. I'm having a problem with my burner shields. I'm getting pretty good sulfur build up on them. I've also cleaned out the burners themselves and had a small amount of the greenish yellow come out of the burners when I rinsed them out. My burners shields have pretty good deposits. Is the the sulfur coming from my gas line or boiling out of the cheap metal (that seems to rust readily in the SoCal damp)? I can get replacement burner shields, but if it's the burners, why bother. I'm likely on the last season for this grill has Any ideas? Thanks.