Well just cold started the truck after getting the PCM flash done. Unfortunately no change to the rattle. Still sounds like a school bus on start up. I did notice that the transmission shudder was gone yesterday on my drive home. I'm going to call the dealer today and see what they have to say about it. Honestly I'm not surprised. Wasn't sure how a software change could fix a hardware problem.
my 18 has the updated parts from the factory...and it too starts like a school bus at cold start up, but as FTO says....it is not cam phaser......mostly waste gate rattle and cold valve train. Only bad when truck sits for 2-3 days +. I dont like it, but I dont worry about it all. just one of the quirks of this truck.
Stop listening for things you think are wrong and just enjoy the truck for what it is.