9Z71 grinding in 4 WD

Could be the axle trying to engage or it could be in the transfer case. Suggest you put it on stands all around and have some one listen underneath for exact location while engaging it.

make sure its not the brakes, also check the right side noise from the front can be deceiving

linkage may need adjusted, try adjusting, truck is 10 years old, if that doesn't work, might be an internal problem, don't think the worst, one step @ a time

OK, you're looking at a CV Joint or Halfshaft that connects to the wheel in question.

Check the front wheel bearing assembleys.

Try removing the front drive shaft from the transfer case to the front differential. With the vehicle on 4 jack stands and the front drive shaft removed attempt to place the vehicle into 4 WD. You may have to start the engine if the vehicle uses a vacuum actuator module to engage the front wheels. When you get an indication that the vehicle is in 4WD try turning the front wheels by hand and see it you hear the same grinding noise .... engage the hubs and try again. Usually if the transfer case is ok then the problem is in the front differential or one of the many universal joints that connect all of the elements together. Check the U joints on the front drive shaft for play as well as the U joints on each of the front wheels.

Watch out! You might have a loose wheel! Check those wheel nuts. If not, a loose brake caliper, or last if not least, a bad wheel bearing. Don't drive it until you find out what the heck is wrong! Could be dangerous.

Most likely wheel bearing or cv joint issue. look for a ripped open cv boot. I believe that year used cv joints instead of regular u-joints. Hope I helped. Thanks

It does not seem that sufficient diagnosis was done. No, you cant give a specific diagnosis like that without tearing unit down. It's likely that they told you the most common failure and left it at that. Likely there is a problem with your unit...I think this becomes more of a trust issue than a mechanical one. A second opinion from an independent reputable shop may help but either way, you need to have it fixed. In not using it much, it makes me wonder how it got worn.
good luck

Bad news... It sounds like you have a broken/stripped axle. I would start at the wheel and start disassembling from the outside in. It may just be a stripped spline in the spindle.