Ok I'm sure this has been brought up before. I own a 09' Lariet 5.9 4x4 with over 300,000 km on it. I was driving it one day and a grinding noise started from the front end. I actuated the 4x4 and it went away, drove a bit more and it came back. Every time I engage the noise goes away.
I've replaced the IWE and hub on drivers side as that is where the noise appeared to be coming from and it is still doing it.

Any help ell trying to diagnose would be greatly appreciated. I'm at my wits end.

 

Check vacuum lines. For leaks with a vacuum gauge try with wheels strait and turned in both directions. My leak didn't show until wheels were turned all the way to the left

 

I'd replace the control solenoid. Its just left of the master cylinder. Statistically, it's the leading cause of your problem.

 

Ford replaced my hubs, IWE twice, all vacuum lines, filters and the solenoid twice also without fixing it.
Last thing they did is replace the transfer-case and it has been good since. But most of my issues happened during winter. Time will tell.

They found a worn collar inside the transfer case...