Do a search for IWE (Integrated Wheel Ends). The IWE Actuators at your wheel will likely be the grinding noise, you need to determine if the seal is gone on one or both of the IWE's, or you have a vacuum leak somewhere else (IWE Solenoid is common as well). Both of mine went on my 2005, my dad's went on his 2006. This is a very common issue and comes up quite often on this forum. I'll see tomorrow if I can find the link but there's a few others that'll likely throw it in there (VTX I think had one).
I can't quite tell in your video but it sounds like the actuators. Is it coming from one or both of the front wheels? The IWE Actuators though will make it go away putting it into 4x4 because what happens is in 2x4 you're using vacuum to pull the actuators in (disengaging the hubs) but with a vacuum leak it can't fully disengage so it grinds. Once you throw it into 4x4 you're locking the front hubs so no more grinding. If you find the IWE Solenoid under the hood and pull the vacuum hose off of it, if the noise goes away you know for certain it's in the IWE system. Pulling that line forces the hubs to lock (front-diff spins) but you can drive around in 2x4 as the transfer case is still in 2x4.
Last edited by homer; 10-18-2014 at 02:14 AM.