Dealer has had my truck for 8 days total now. They replaced my IWEs, my transfer case, and today they said they knew the problem!! It was a wire, but they didn't know which one (I was guessing it might be related to the solenoid). Ford Hotline told them it had to be "this" wire. I was excited. Five hours later they call and say it didn't fix the problem and they are still stumped.
The dealer was smart enough to thoroughly test drive after each fix attempt. They said it worked fine the first four times they engaged 4x4 Hi, but on the fifth try it was grinding again. They ordered another new part yesterday - I was so numb I don't even remember what part they ordered. It was installed today and still didn't fix the problem. The dealer is running out of ideas (or they screwed up one of the fixes that should have worked).
At least they are experiencing the problem and know something is wrong!
To clarify my issue:
I can engage my 4wd Hi if I'm stopped (or even less than 5 mph). I can drive in 4wd with no issue and disengage at any time at any speed.
If I engage 4wd at any speed higher than 5 mph, I get the grinding noise in the front end. The noise continues as long as I stay in 4wd, but I can switch back to 2wd and the noise is gone.
Hopefully at some point they just order me a 2013 to replace my 2012.