Sharp clunk from transfer case when shifting into 4x4(esof)

[Metalingus]

If I lock the front hubs and drive, shifting into 4high results in a sharp clunk from the rear(ish) area of the truck. Is this the transfer case? I recently greased the front hubs and I can feel them engage smoothly. Problem is, when I switch off 4high, the system stays engaged until I slow to about 20mph. Then it all disengages. It's a 450 with auto and esof. Hoping to get some input before I drop it off at the dealer for some troubleshooting. Hoping for the best.

[AllGo'N'Show]

They are definitely super slow to disengage, check your lines for vacuum leaks may help this process speed up but I believe the pump runs for almost 60 seconds at times, not sure how long they estimated the actual engagement/disengagement should take.

Click from the rear would depend how far back, could be transmission, u-joints, rear end, anything that moves as you go back. Can you get a buddy to help you by doing the shifting if you are underneath it and figure out where it is coming from?

Subscribed to see some more long term owners opinions as well.

[Metalingus]

I'll start checking around. Forgot to mention the aforementioned noise is speed dependent. The fast I am going, the louder and more harsh it is. The manual claims that 4x4 engagement can happen up to some 45mph. If I did that, I swear it sounds like the tc is going to grenade. It's been so harsh in the past that the whole truck has jumped. And this is a f450. Couldn't get it to the dealer today but I'll update as I can. I will say that greasing the auto hubs definately makes a difference. Super smooth to engage, just don't know what that reward smacking sound is.