Transfer case , auto hubs or trans noise
 

I just bought a 95 Ram cummins 4x4 5 spd. Drove it home at speed,150 miles, in 2wd no sweat. Backed it up in 4wd to park it , put it back into 2wd and shut it down. Next morning, I set off to get it inspected and began hearing a sort of grinding sound, like gears trying to mesh, periodically in any gear as I was driving, The trans did not seem to be acting abnormally as the truck kept cruising smoothly along. The sound would come and go.
A friend suggested that perhaps one of the auto locking front hubs was attempting to lock even though the transfer case was in 2wd. The transfer case was replaced before i bought the truck aand judging by theother repairs done to this vehicle it was likely done right.
Anyway, I am afraid to drive the truck for fear of doing damage. Any ideas as to what and where I should look to try and figure this out? Truck has 172k miles mostly local pavement transportation.

Check your CAD shift actuator. There is no way an autolock hub is messed up because these trucks have none, the fron axle is disengaged by the CAD, Central Axle Disconnect. It is the piece that is on your front axle pass side between the pumpkin and the hub. I say check your shift actuator because before I fixed the shift fork I had problems getting it to disengage and it would make a similar noise. Make sure your t-case is not engaged and if the front driveshaft spins this is most likely your noise.