Is it a differential or a transfercase or both?

[spud]

I have been dealing with what sounds like a rear diff howl. The warmer it gets the louder and mainly under acceleration with a more like growl as the speed reaches 20mph or less under deceleration. Now why I have shifted my mind to the transfercase as an option is #1 when I have had pinion bearing slap before i could make the rear end make a clunk (lack of a better word) by jabbing the fuel and letting off immediately in other types of 4x4's. #2 I just recently noticed that when I first take off I can get my transfer case to engage (using the selector switch, can hear the solenoid clicking and the indicator lights in the cluster come on and off when I engage the 4x4 and when I disengage it). After a few miles and the howl/whine of the (thought rear end) is good and loud if I try to select my 4x4 to engage nothing happens, no solenoid clicks no lights and no 4x4. I can park for an hour or so and nothing, still not working but if I let it sit for a very long long time (like over night) it again engages and clicks and lights just like it should.

I had the truck services at one of them quick lube type places and I asked all fluids be checked and they stated all was fine but I can not be positive they did check the fluids and me being a gimp i can not do it myself.

So I know of a guy parting one out that has the diffs and a tcase, I am not rich, if I was I would saw screw it and pull both diffs and tcase and swap out so with whats has been said if you had to bet on what was wrong and hit blindly what would ya shoot for, the diff being bad or the tcase?

 

[BIG GREEN FORD]

Diff.. my f150 is 2wd and it does the same noise.