You might check the tightness of the bolts holding the front axle in place. There is one big one in front that attaches it to the front crossmember. See if its loose or if the bracket on the crossmember is damaged, I've seen a few of those break. But if its making noise in 2WD w/ hubs unlocked, then its likely something else, since the front axle and drivetrain would not be moving. Perhaps motor or tranny mounts are loose?