Was driving my 99 ram 1500 5.9l up a hill in snow yesterday in 4h. All of a sudden I heard a banging noise sounds like some hitting the under side of truck with a sledge hammer. When I take it out of 4x4 the noise goes away. 4h or 4l doesn't matter. When the truck is in 4x4 and I accelerate hard the banging is faster kinda like something hits a certain spot and binds for a second. When I let off the throttle the noise goes away. I checked my fluids and my transfer case was bone dry. I filled it and nothing changed. I took my front drive shafts off inspected it and all is good I drove the truck in 4x4 with shafts out and no noise so it happens under load.

​​​​​​​I'm thinking from differential or tcase bit I'm not sure how to diagnose it. Any help is greatly appreciated

 

Probably the chain in the t-case is stretched out, and slipping under load. You *might* be able to get away with just changing the chain...... find out when you have it apart.... If it's your only driver, replacing the case might be the better way to go.

You can verify its the tcase by having some else drive slowly, while you listen to where the noise is coming from.

 

I did that and it echos through the entire under side. I have a new tcase for it on its way today. My first thought as well was the chain slipping under load as well

 

my 99 did the same thing before I had my transmission and transfer case rebuilt. The shop said my chain was stretched and was slipping on the sprocket