Transfer case whining

[BIGBLOCK24]

ive got a 2002 chevy 2500 4x4 with 8.1l and Allison transmission. I drive this truck a good 200 250 miles a day,and I been hearing a somewhat loud noise for pass week and sounds like it coming from

transfer case.it still drives fine only thing is now it wont shift into 4low.Is this something I need to address right away

[LongrangeLauber]

Sounds like a bearing going bad. I would get it checked out before the tcase (could possibly) grenade. As for the 4LO my guess is that maybe the actuator is going bad? I would have the dealer check it out, take it for a test ride with the shop foreman