Weird new symptom: gear quietly grinding

Maybe tap around any skid plates, or heat shields to see if anything is loose, touching a moving part or has a rock trapped.

Then start by checking your transmission and transfer case fluid levels. I would suggest doing a drain/refill so you know those are good. Be sure to inspect the fluids for excessive metal particles.

Drive and recheck for the sound.

Then replace the clutch fluid and thoroughly bleed the system.

Drive and recheck for the sound.

If after all that, you might want to stick a GoPro in various areas around the drive train and record the sound.

Something should reveal itself by then. If not, maybe it's time to have a Pro take a looky loo at it.