Knocking on startup

Hello Guy's/Girls first time posting here as I'm new to the forum
I have a 2016 F350 Lariat
The engine has only 2900 miles on it.
At idle cold it has a loud enough knock that is in conjunction with engine revolution, when it's warm the sound is about 1/2 to 1/3 as loud. When I took it to the dealer it had warmed up and the sound was gone.
If I shut it off for an hour it comes back and then disappears after running it a few miles. I have even heard it come and go while idling. It seems to be loudest on the drivers side front.
Checked the fuel/water sep. clean as a whistle.
Use Standyne cetane boost in fuel and all fuel has come from commercial stations that have good rep and go through tons of diesel fuel.

Any of you have this.
I have 14 pieces of heavy equipment All diesel (industrial) I never had one of this complexity maybe this is normal? I didn't hear it doing this when I picked it up from the dealer new, which was only 2900 miles ago, but maybe I wasn't paying attention???