2007 F350 Clunk on 4x4 Engage!!??

[Mudvayne]

Hi guys a quick search returned nothing on newer trucks.. 2007 F350 6.0 H-D Edition- 81,000k. I bought the truck at 75,000k and I know a little about its history but when I switch to 4x4 high moving around 30-50k I get a harsh clunk like can feel it in my feet..any ideas or anyone eles have this problem I have not poked around under there yet thought I would ask here first to get a direction to look in!?
Thanks in advance.

[trucktractorman]

30-50k??? Dang what are you hauling?? yea that switch is only a vacuum line that temporarily locks the hubs. For tough situations it is encouraged to manually lock the hubs. I too have the clunk, but only when i go from 4 high to 4 low.