Welcome to Justanswer, My name isXXXXX am here to help.
Do you have any issues with the vehicle running?
How did you verify the location of the noise? Does it sound internal of the engine?
vehicle running fine mechanic traced down noise with stethoscope sounds internal coming from bottom of oilpan
Well the problem could be an exhaust leak. On these trucks they can do there is nothing in the bottom of the block that will cause ticking noise but if the issue is a lifter tick this can travel to the bottom
Does the noise go away ever?
definetly not exhaust leak noise heard more after it heats up could it be main bearing or rod bearing
Normally if this is the case it will be a slapping noise not ticking
But I would remove the oil and check for shavings then remove the pan and inspect all of the caps if one if damaged you will find wear
it is more of a slapping noise thought it was timing belt at first but it checked out ok
Then it is possibly a rod or main more common for a rod cap but drain oil drop the pan and check if you find one and its saveable you can replace the bearing but if its bad the engine will need to be rebuilt.
can rod bearings be checked by disconnecting one spark plug at a time to hear if noise goes away
Sometimes not always not a very accurate way to check
any test for mains
Because the cylinder will always be in motion so it will not go away but if the noise is very loud when you do each one and find the one thats bad it can quiet down some
Pull the oil pan
Thats is the best way period first if there are shavings you can bet on there is damage
But if you cant tell for sure then you will have to check each one turn the engine over until each one is pointing down then move it up down should not have any movement if so its bad pull the cap and check the bearing