White Haze on Cast Iron Stove Grates?

I have a Wolf gas stove/oven. I have always cleaned the cast iron grates by spraying with oven cleaner, leaving them to soak for an hour or more, then rinsing off. I found this tip somewhere on the Internet years ago. It worked great! All the grease and anything stuck on, rinsed right off. However, all a sudden I'm noticing a white haze on them in spots. It's highly noticeable. I have tried everything to get it off, scrubbing with a wire brush, soaking in ammonia (which is also a fantastic way to clean them), and plain old soap and water with a tooth brush. Nothing is taking it off. And I can't seem to find anything on the web to help me figure this out. I even called Wolf themselves. It's driving me crazy. Does anyone have any clue?