I had one years back making the noise you describe..keeping in mind noises are hard to describe in print..And it was a U-joint in the front shaft.When put into 4x4 the front shaft made a noise as the play was taken up..it kinda thunked.
It could be heard when first putting it in 4x4 AND when going from reverse to drive and the play in the joint went in the opposite direction.
But again noises are tough to pin point when all you can do is decribe them in print form.One mans cluck is another mans pop.

 

so it doesnt do it at all in 2wd?

 

I was thinking U-Joint to but I just put new ones in Saturday and it didn't help at all. Have changed both CV Shafts as well.....

 

It does ot do it in 2wd at all. Truck runs smooth with no problems in 2wd. Guess I'm gonna have to take it into a shop and just pay the fine for them to figure it out and go from there.... That sucks tho

 

Is it a rhythmic clunk or is it random or does it only happen once when you shift. Does it happen only when driving straight or turning? In reverse?
Does it happen when you are coasting, cruising or just under application of the throttle?

.

 

Fords tend to do funny things like that. Check your CV's and U Joints. Welcome.

 

wonder if the Aarm bushings are bad..i would think it would do it in 2wd though...but i guess the 4wd could put enough resistance on it to make it make the noise then