Either you have the rattle at cold start or not.
Mine developed at roughly 41K, I am currently at 42K. It only manifests itself in my truck after letting it sit for a week or two, then only on the first start for 3 seconds or so..........It sounds like a diesel engine then runs and performs flawlessly.
Mine also doesn't do it consistently, I wasn't going to bother with doing anything with it as it is just an intermittent noise for 3 seconds at startup. I got the letter this week and figure I'll give it a shot. I'm certainly not rushing to the dealer today.