I'm not sure if it's the transfer case, but the squeal I'm hearing is coming from right under my *** when I'm driving, so, that's transfer case.
The noise sounds like a belt squeal. Only happens in 4WD, only when moving. Gets faster as speed picks up, slows down as speed decreases.
I have not checked anything yet, bit I know the transmission is full, I check that regularly. I changed the front and rear diff fluid less than 2 months ago. I have NOT checked the t-case fluid level, but my initial thought is that the fluid is low. What type of fluid does it take anyway?

Does that make sense? I've actually never heard a truck make this noise before, so this is new to me. Truck does shift into 4x4 no problem.

2000 2500 4x4 cummins

 

Never experienced a squeal from a transfer case like that...but maybe checking the ujoints for play is a good place to start since that can be done without really tearing into anything.

Btw, i believe the fluid is atf +4, same as the transmission (assuming its an auto)

 

Put the same ATF in the trans. case you put in the trans.

 

Got it, yes it's an auto. I have checked the u joints recently as well. No play there.
I keep an eye on the u joints and fluid levels (for the most part) pretty regularly because I tow frequently.

 

its probably the double-carden u-joints in the front drive shaft.
you can prove it by removing the front drive shaft and operating in 4wd.

if you don't want to rebuild the joint yourself, take the drive shaft to a drive line or machine shop.

http://www.pavementsucks.com/tech-article-16.html

 

Even if it is a manual... the 5 speed manual also uses atf.

 

I'll give that a shot.
Thanks