I posted a question back in July regarding a know that I heard while at idle. Many suggested that it was the injectors. You were correct, I heard the injectors but I also heard the knock. I took my FX4 Ecoboost into the dealer for the 3K mile check and let the maint tech listen to the engine knock. He heard it and worked with Ford to go through a large list of possible options. After three weeks and a brand new Ecoboost engine in my FX4, it was a wrist pin failure in the #2 cylinder. Ford paid for everything including three weeks of a F150 5.0L rental. I have driven it two days now and it is much more quiet and seems to have better performance. Time will tell regarding longevity. I will keep you all posted.