Mine is definitely either the Transfer Case, or the Front Diff. The noise goes away with the application of 4wheel drive. I'll hopefully find out tomorrow.
Mine is the exact same as yours. Not only does the noise go away in 4HI, but going back into 2HI there is a bit of a 'thud' which sounds similar in to the noise heard when driving.
I'm dropping the vehicle off in the morning at the dealership. Hopefully they can finally track this down.
Rob