Guys, I need help!

My 96 ram makes a grinding noise that goes away when I try to put 4wd Hi in without having to engage it completely. It will go away for a while and will come back again.

The only way it goes away completely is if I change the vacuum lines and leave the C.A.D. engaged and the 4wd light on. I can drive around like this (transfer case not engaged in 4wd) and it dissapears.

I'm thinking it could be a bearing in the axle?

The vacuum switch in the t-case work fine, the vacuum motor works fine, I have checked all these parts from top to bottom. It only leaves me to believe that it could be something on the axle. I have also taken offthe front axle drive shaft and it still makes the sound if left in 2wd. Pulling the lever on the t-case will not make it go away, I need to engage 4wd for it to go away.

Any help on fixing this?

thanks for reading...