What are symptoms of the whine? On-throttle only whine that goes away when you lift off the accelerator? A whine in any gear at 35+ mph? I had a whirring noise when in neutral and coasting at low speed (inaudible at speed). Eventually the whine turned into a marble-in-can sound.
Do a fluid change first (see what comes out).
Does it sound like this
(start around 14 seconds)?
If so, it's most likely the center differential transfer driven gear bearings. $133 or so in parts cost to replace the 4 in the center differential case extension. The good news is (if you've got time and tools) that you can DIY this job in a weekend. You will need a shop press and a set of punches for roll pin removal (I used a set from Lowe's).
Here's the NASIOC thread
on the issue.