1996 JGCL 4.0 L6
Automatic
Selec-trac 4WD
110,000 miles on the drivetrain.

Been having an intermittent "thunk" noise on startup - seemed to be from the right side floor pan under the seats - figured it was a failing trans mount and have been trying to find time to replace but have not done yet.

NOW - this morning, I am getting a weird "popping" noise from the trans/transfer case area. It is not constant and is not very loud either. If the radio was on or the heater on full it would be hard to hear. the noise is worst with the trans in drive, stopped with the brakes on. It almosts sounds like the torque converter is trying to lock up or a bearing in it is going out or catching. The noise gets less intense when i put it in neutral and it got less intense and frequent as the truck warmed up on my way to work. It makes the noise whether stopped, in motion, in park, neutral or any gear selection on the shifter. I did not try putting it in 4WD yet as I don't want to blow out whatever is starting to fail.

The transmission shifts and drives perfect. there is no lurching or other identifiable slippage.
Whatever it is - it must be a part that is in constant motion when the motor is running regardless of transmission shift position or relative motion of the vehicle but the failing part also must be under load when the truck is in gear as the noise is noticeably worse then.

This is my daily driver and while I am a "car guy" with my own tools, jack, jack stands, etc. I don't want to start guessing and replacing parts until i find the right one as I'm not rich either!

Any help would be greatly appreciated!!

 

Universal joint, perhaps? slide under there and give the axle a twist. It may be obvious, but sometimes not. A tiny bit of movement will translate into sound when a load is applied.

 

You want to make sure the bolts aren't loose on the flywheel first cause that could be catastrophic. Next check that the slip yoke is greased. Then move on to u joints , but you said it happens at a stop in neutral...So many other things that are not driveline, like brakes, for example..