heres the problem. while the truck is coasting there is a horrible vibration and loud hum coming from the rear end. the weird thing is any throttle at all makes it stop even the wait of my foot on the throttle. i have gotten out a few times and put my hand on the differential and its pretty hot. any ideas?

is there fluid in the diff and is it filled to service level? Could be bad pinion bearing or bad ujoint on the pinion yoke.

check your oil level if its full look at the pinion bering its developed some back lash some how pinion bering i think is the rascel.

Actually, check the center carrier bearing also, i had mine fail and it did the same things you described. I even did a write up on how to replace it. Still good to check out the rear diff as well. http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/28-transmission-systems/244-driveshaft-center-carrier-bearing

Thanks for all the replies guys. Was wanting to get into this weekend but I work about an hour from home and leaving work it's started popping and clicking real bad. Knew I couldn't make it home so I had to leave it at shop. Guy said it's more than likely pinion bearing

Good time to replace all bearings while your in there.

while he has the diff apart he can inspect the ring and pinion to ensure its not damaged. good luck!

Sounds like the same thing I had when I first got my truck. I lost a tooth on the pinion gear, made plenty of metal and lots of noise similar to what you described. GB