Howling noise while in 4 wheel drive

[Coty]

I’ve got a 2003 Silverado that makes a loud howling noise while in 4 wheel drive and in auto 4x4. Noise gets louder when I accelerate and goes away when I let off gas. Can also feel vibration under drivers side floor board while accelerating. Anyone have any ideas what this could be or where to start? Thank in advance 

[diyer2]

Howling noise?

Transfer case chain?

Vibration?

Transfer case shaft problem?

 

[Coty]

Think it could be U-joints making noise?

[oldmann]

They did this from new.  Even a new truck makes a different noise with the transfer case engaged. 

[sdeeter19555]

They did this from new.  Even a new truck makes a different noise with the transfer case engaged. 

The 2500hd's with the manual transfercase shifter even have a TSB on 2wd/4wd noise, that there is no fix and it is considered normal.

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[PTXer]

Coty, Mine does the same thing.  Since I just bought it a few months ago not sure if it's always done this or not.  Plan on changing the fluid when it gets warmer.