Whine from Transfer case? - MPH related, not RPM

[CWOLAW]

98 expy EB, had flashing A4WD light. Dealer replaced both Hall Effect sensors. That solved the flashing A4WD Light issue, but now, I have a whine that sounds like it's coming from the transfer case (drive past some jersey barriers with window down, and you can really hear it - it is affected by Speed (MPH) - go faster, pitch increases, slower - pitch decreases. It is not affected at all by RPM Changes - if I down shift or turn off OD to increase RPM's, sound doesn't change as long as speed remains constant. Also, interesting enough, after orginally noticing this upon picking up the truck from the dealer, I had to travel and leave truck sitting for a couple weeks. Returned home to temps in the upper 30's / lower 40's - about 30-40 degrees colder than when I left). Sound was not evident when I first drove the truck in colder weather, until truck was driven approx. 10-15 miles and well warmed up, and then, there it was! The same whine. Any thoughts?

 

[Whack]

New or Old Transfer case fluid?

When warm does it make the same noise in 4LO?

 

[CWOLAW]

I haven't changed it and I doubt the dealer did in the process of changing out the hall effect sensors, so I have to say, Old. The sound wasn't there before the hall effect sensors were changed out. It is now.

Intersting thing now - they can't "reproduce" the sound. I now have the truck back, and sound is not there, even when warm. Too Weird.

 

[CWOLAW]

New or Old Transfer case fluid?

When warm does it make the same noise in 4LO?

P.S. - Didn't try it in 4LO. But will.