Grinding in and out of 4 wheel drive

I guess you probably don't know what transfer case you have ?
SERVICE 4WD
Refer to
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Transfer Case Description and Operation in Transfer Case - NVG 149-NP3

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Transfer Case Description and Operation in Transfer Case - NVG 246-NP8

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Transfer Case Description and Operation in Transfer Case - NVG 261-NP2

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Transfer Case Description and Operation in Transfer Case - NVG 263-NP1

The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral.
The four manual mode, or range gear positions, of the NVG 261 transfer case are:
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2HI - 2 wheel drive high range

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4HI - 4 wheel drive high range, part-time

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4LO - 4 wheel drive low range, 2.72:1 gear ratio reduction

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N - Neutral, 4 wheel

The NVG 263 transfer case provides the driver with 4 manual mode/gear positions:
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2HI - 2 Wheel Drive high range

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4HI - 4 Wheel Drive high range

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4LO - 4 Wheel Drive low range

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Neutral

With the info I've given you ,you should be able too now !
There is probably a code stored somewhere !
DTC B0790 DTC B2725 DTC C0300 DTC C0305 DTC C0306 DTC C0321 DTC C0327 DTC C0359 DTC C0374 DTC C0379 DTC C0550.

May be the problem is not in the actuator in the case but in the actuator that engages the hub locks . Check for vacuum line / electrical wires faults . The noise may be from the hub lock or from a cv joint in that side.

Check the oil in the transfer case. If it has lots of metal in it... time for a new one. They aren't the world's strongest.
Another check: Lift the front of the truck, while keeping the rear wheels on the ground. Engage the 4x4 switch (then turn the truck off) crawl under and try to turn the front driveshaft by hand. If it turns and the wheels turn, the transfer case is the problem if it turns but the front wheels don't... front diff issues. Any grinding, crunching etc is also a clue.

There would also be a 4WD switch on diff

well typically is there is a noise when making a turn its caused by a bad cv-joint but if your having problems with the 4 wheel drive i would look at the linkage to the transfer case and make sure there is not to much play or bent or broke rods and stuff.

4wd fuse is good. Check the switch on top of the transfer case. This is what sends power to the actuator.

I had a similar problem and had to have the 4 wheel drive serviced. It need new grease. the grease i had was old and it was causing the gears not engage cleanly thus causing the grinding sound until they were realigned.

need to check wheel bearings

it duse not sound good. sound like your tranfre case is on its way out.but i would have it antillies frist you may have a bad sencer

Your trouble is most likely not in the transfer case but in the front differential engagement solenoid.