2016 F250 FX4, 6.2L/6R100, 56,000 miles, Customer complaint of a "Bell Sound" in 4 wheel high....He heard it during the ice storm we had a couple weeks ago while using 4WH.
Confirmed the noise in 4WH, Sounds like someone is dropping pieces of steel on the ground right under the driver seat. Interestingly enough no noise was heard in 4WL?
Racked the truck & looked for anything loose, Vacuum tested the hubs & they appeared fine. In fact everything looked perfect & payed special attention to the front shaft U-joints., T-case & front diff full of fluid. Took it for another test drive, manually locked the hubs but left the T-Case in 2WH, Noise still present.
Unlocked one hub at a time & it seemed to make the noise more often with the right hub unlocked & the left hub locked, But it was hard to tell the noise was sporadic anyway.
Racked the truck again, Spun the front drive shaft again but I guess a little faster maybe out of frustration, As I spun it several times checking the U-joints. And I heard a metallic clang. Difficult to recreate spinning it by hand.
Took some rope & ran several rounds on the DS, Pulled the rope hard as I could while keeping my ear close to the shaft & the noise was far more audible.
Remove the front DS....Shook it, And it has something loose inside the tube

.....Like a 1/2" bolt or something. Having the DS cut open tomorrow & I'll report back with what's found inside.
Still wonder why I didn't hear it in 4WL, Maybe I didn't get up enough road speed?