DAC68

Recently bought an 01 Excursion ltd, v10, 2wd, 126K. Starts great, accelerates fine, no smoke, good oil pressure, clean oil, no hesitation, no warning lights, good fuel mileage. It sat for about a year with the previous owner.
But, it has an odd sound upon acceleration or creeping up a hill (waiting in line at school). It sounds like an intermittent misfire. It's sort of a popping sound. It will somewhat replicate the sound in neutral at around 2-2500rpm.
I replaced the plugs, they were ok, ready to be replaced, but not bad. No change. Still noisy.
Wife doesn't like the extra noise. She's used to here denali. I looked at the exhaust manifold gaskets, they look intact, to extra soot. The donuts, from what I could see look ok. I don't feel anything with the engine running coming from those joints.
Could it be a leak under pressure? I'm sort of at a loss. Any help would be great! Thanks!

R.S.LOGAN

Could be leaking with the engine movement as drive taken up . Check the manifold itself , also block tailpipe with a rag when engine running and see if any leaks show .

DAC68

Good idea. I hadn't thought about the twist. I was going to have the better half help, but thought better of being underneath while she was in the driver's seat.....

R.S.LOGAN

Play safe and just get her to block of exhaust tailpipe .

DAC68

played safe, had the Admrial plug the exhaust. No leaks. Good friend, mechanic said ' catalytic converter'. Had checked, not broken baffle.
The noise is coming from the top of the engine. It happens when accelerating or idling above 2K. Most notable when reving from 2-2500. It sounds like a hollow detonation. You can feel it in the intake. It is getting more noticable now. The fuel mileage is now suffering.
I am very confused about what the problem could be.
Had the torque converter checked, the flywheel looked at (with a probe camera).
One person thought it was a rod bearing or cracked piston skirt. I'm not argueing, but wouldn't that be making noise consistently? Wouldn't the oil pressure drop? It stays in the top half of the idiot gauge all the time.
Could this be a computer or timing issue? We did a rough cutout test by unplugging the coils one at a time. No change.
Totally baffled, as well as half a dozen professionals.
Thanks,
Doug

R.S.LOGAN

It's not " pinking " / pre igniting due to timing being over advanced ?