I have a 04 ram 2500 crew cab with 170k on it and i have just developed this problem. When the snow arrived here i switched in to 4wd and heard the noise. It happens on de-acceleration, it started when backing off the throttle at 100kmh now it does it at 30kmh as well and that is when you really hear it. It is a loud deep growling noise and the vibrations can be felt through the truck. I have tried it in 4 low and it still does it. I found a front axle joint worn and noisy so i changed that but the noise was still present.

If i run it up on the hoist i cant really get it to make the same noise, i did hear a noise in the rear axle that was similar, the noise seamed to transmit through the axle tube so i removed the half shaft on the left hand side where the noise seamed worse but could find nothing wrong with the bearing on the hub.

I have changed the oils in the diff/transfer and the box. When checking everything i have found there is slight up and down movement in the output shaft going to the rear, where it attaches to the prop shaft (front to rear axle). I also noticed that there seams to be a lot of backlash if that is the right term, when you turn the rear prop by hand there is a probably an eighth of a turn before the front prop reacts.

i hope i have given you enough info to help, if you need to know anymore then please just ask.

Also i have noticed now that there is a slight whine in 2wd when backing off the gas but nothing like when it is in 4wd.