Re: 4wheel drive problem
Sounds like the forks in the transfer case are slipping. If you have an electronic transfer case knob on the dash (not a lever on the floor) then the fault knowingly lies with the TCCM, or transfer case control module. The module is located between the front seats under the dash. In some vehicles it's fairly easy to access, others...not so much.
I'd get this checked out before a fork snaps off in the transfer case requiring a rebuild.
If you're due for an axle fluid change, removing the covers, cleaning the magnets and inspecting the gears will rule out any clips/debris that could have caused damage. Then you'll have to seal it up with RTV sealant and refill with fresh fluid. I strongly believe it's the TCCM, or transfer case in general that's causing the noise. Even with the front axle disengaged from putting power to the ground, the front differential still turns with the speed of the front tires/wheels.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!