Popping sound from undercarraige

Year: 1999
Engine: 4.0
Transmission: Automatic
Transfer Case: NP231

The popping is sometimes soft, but other times hard and I can feel it through the floorboards. It happens when I am accelerating and also when I am decelerating, pretty much when there is a transfer of weight. I was initially thinking it was the suspension in the front, but after a pretty thorough look I did not see anything that could be causing the issue. I continued checking the undercarriage and eventually I shook the transfer case a bit and it had some play to it, and one time it popped. So now I am thinking it may be the transfer case mount. Any ideas would be greatly appreciated.

A worn out transmission mount would be a good place to start. I would also recommend double-checking all of the suspension components to ensure that the bolts are tight.

I had a similar popping noise that occurred when the vehicle pitched forward and backwards... turned out to be the pinion u-joint on the front drive shaft. Replaced it and the noise went away. Might be another thing you could check...

Is it at all possible the exhaust pipe is contacting the crossmember? There's a very small clearance, and if the mount in the crossmember is starting to deteriorate, it will allow the pipe to touch the crossmember, especially when the drivetrain is shifting due to torque loading and unloading. Just went through this with my '96, the the one-year-only rubber block is not available. I had to make a new block and hanger from other year's parts. Hope your '99's is available.

Thanks for the ideas, I will check out those areas and post back if the problem persists.

i would also double check the motor mounts as well.

transfer case linkage is knocking. Lube well and/or replace the bushings.

I just finished upgrading my crappy rocky road adj. Tracbar to an iro double shear one and that got rid of my popping. I could feel it right below my foot on the floor boards before doing this.

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