I have a 2014 Dodge Ram 2500 standard cab long box. It makes a gear howling noise in 2wd only. In 4wd the noise goes away. Dealer already changed the transfer case and it made no difference. Now the dealer is stumped. Anyone else having this problem?

I have a 2014 Dodge Ram 2500 standard cab long box 4x4. It makes a gear howl noise in 2wd only. When it is in 4wd the noise goes away. It doesn't matter if I am accelerating or decelerating or turning or going straight down the road. The dealer already changed the transfer case but it didn't...