pop noise on acceleration

I have a 97 Xj completely stock. When I accelerate from a stop I hear a pop noise under the console. Sometime when backing out my drive I also hear this noise. When running down the road it never makes a sound. I'm planning a long trip and wondering if something is about to break. I've crawled under and can't find anything loose. Occasionally when accelerationg up an incline I will hear the pop sound. It's not loud just annoying enough to make me wonder what is about to break.
I took it to a mechanic friend and he can find nothing wrong but the pop continues. I have a pop free 96 so I know this is not a normal sound. Any ideas. I did search and didn't find anything that was helpful.
The drivetrain has about 125,000 miles on it..Just a guess as I have a new engine and cluster which shows 27,000. (had 10,500 when installed)
HT

sounds like your transfer case chain is stretched. Mine is stretched also. It pops under hard acceleration.

Another question dead in the water. Guess I'll bungee myself under the Jeep and give her the gas so I can find that noise. POP now sucker I'm under here watching you.
HT

badbowtie87 said:

sounds like your transfer case chain is stretched. Mine is stretched also. It pops under hard acceleration.

Click to expand...

Guess I posted my sarcasim a little too soon. Thanks Badbowtie87.
HT

How old is your oxygen sensor?

If it's beyond the useful life, it can react slower than it should. Under certain conditions, this allows the mixture to go extra rich, the unburned fuel goes into the exhaust, and you get a small POP similar to backfiring through the carburetor when the unbrurned fuel hits the catalytic converter.

I'll take a wild guess that you've never replaced the O2 sensor, which should be replaced every 75,000 to 80,000 miles.