I've seen various cars that:

Had a bad drive shaft center bearing / mount that usually spun OK but sometimes bounced around. ( Think of a electric motor with a bad bushing )

Inner tri pod style CV joints no longer hold the center shaft concentric with the housing.

If your drive shaft has rubber drive discs, have a look there.

My 97 C280 suddenly developed a ZZZZZZ sound after driving on a road where someone drove a track machine rippling the pavement. The noise when away after stopping but came back / went away ~ 15 miles later. I knew it was transmission planetary related as I have head this before. Pulled trans , rebuilt , replaced worn K2 bushing ( between front and rear trans shafts ) no noise for the next 8 K miles. 99 should have an uprated K2 needle bearing to solve this problem.

The transfer case might be making noise, I've had a planetary noise before. The transfer case should be Borg Warner and similar to Ford.