Crackle sound on acceleration

98, 4.0, 5spd, ax-15, np231j, d30,8.25...

I'm getting a crick crick crackle type noise under loaded acceleration only every once in a blue moon when starting the jeep. It only occurs in first gear, and it only occurs only after start-up, approx 1500rpm about 300 feet out of the driveway, and only occasionaly... should I be looking for an exhaust manifold crack? If so how can I diagnose other than visualy?
Also, and please dont :flamemad:, I am broke and running straight pipe from header to the muffler.

The exhaust manifold is subject to cracking due to engine torque (twist) while under load
or acceleration.

I would first look closely at where the primary tubes join the collector. Look for any odd
white powdery deposits, at or near the welds in that area. Usually there's a hairline
crack near those deposits. Also, the sound could be coming from the collector bolts,
or the collector flange.