This is what I would do to check it...There might be easier ways.
Put the front end up on jack stands, make sure the hubs are unlocked, try to rotated the tires, watch the axle, if the axle turns, then the hub is not unlocked(seized or something). Then make sure the TC is in 2hi, and try to turn the front driveline by hand. If it is truly disengaged it should spin fairly easily and the front tires shouldn't rotate. If all that is true then your front diff is not doing anything while you are driving in 2 hi with the hubs unlocked and the noise isn't from the locker. If any of that is false, then you have problems with your TC or front hubs.