You're not alone. I have the same F250 CC model, nearly the exact same issue and posted a few weeks ago on it. Mine usually happens around 1600 to 1800 RPM when casually accel'g. from a stop. Doesn't matter what gear it was in - when 1600-1800 RPM was reached clatter, clatter, caltter!! The odd thing was that, if I kept it at that RPM and speed, it was an inconsistent type of hit-n-miss hammering until I accelerated a little more and it became more consistent with the engine RPM. Once I'm in 4th and cruising at about 1900 RPM on the highway I don't hear it.
I only started noticing it since the weather has turned cold here. I bought it this past Aug. and had I heard it then I never would have bought the thing thinking a rod or something else expensive was going south
From what I can gather from all the good folks on here
seems there could be a couple of reasons for the type of hammering, 1) air in the fuel stream from the fuel tank line connectors, 2) bad injector or two, unbalanced HPOP oil rails (IH design issue), HPOP internal leakage (oil bypassing internally) to name a few. (There's probably more).
I haven't pulled any codes yet - that'll take a trip to the dealer when time allows.
I am going to try the HPOP oil crossover mod, regulated fuel return mod and possibly an AirDog or FASS filter pump system to deal with any air leak issues. Besides reducing the clattering (cackle) and the starving of no. 8 injector (IH design), I'm told those mods are supposed to help out with the overall engine performance such as improved throttle response also.
Hope others will chime in here on this.