First off the vehicle is a 1995 S10 pickup but I'm posting this because its the best board Ive found and its the same driveline. The 4.3 has a 115000 miles on it and it emits a rather quiet popping sound. The noise occurs if u rev the truck to 1800 in park but it is the worst right as the revs start to increase and when the rpms return to idle. The noise also occurs whenever the a load is put on the engine. The motor still sits in at 200 degrees and has plenty of power. Ive checked the valvetrain and nothing there appears to be causing the problem. and I plan on checking the timing chain next but i was wondering if anyone had any input before i do all that work. I also talked to two mechanics about the issue and one said it was wrist pins? and the other said just drive it.

 

Not sure what the problem could be but try Lucas' oil substitute. replace a court of oil with that next oil change it might free stuck parts or cause them to slide arould smoother in the engine.