new squeak/whirring while in 4wd only

Hi guys, I searched past threads for about 4 hours and haven't had much luck finding the answer, any help appreciated..

I have a 2012 4 cyl SR5 4wd. 210,000 miles, almost completely stock. Every week when I visit my parent's farm, I engage 4wd for a bit (dirt roads only) to exercise the 4wd system for a mile or two. Today though, I heard a new squeak/whine that seems speed dependent coming from underneath. It only happens in 4wd, so i am thinking front driveshaft or Transfer case. I grease all the ujoints every other oil change, and the Tcase and front diff fluid were changed about 8,000 miles ago. Never made the noise before, and the noise went away when I went back to 2 wheel drive. I am hoping I don't have a transfer case going out on me. Anyone have any ideas? Thanks

 

Is something wrapped around the shaft or the axles, have you gotten underneath and looked? Have you checked for play?

 

Yes I think it must have been a stick or something. I tried the 4wd today in the yard and it didn't make the noise.
I crawled under afterwards and couldn't find anything, no play, etc.
It's due for an oil change in about a month, I'm going to grease and check everything under there real good when I get it on jack stands.