Since the pop is associated with the starting of motor, I am wondering if the starter itself is a cause. Is there a mechanical part that would make a metal-to-metal pop?
A close sound reference is...
When engine idles and you mistakenly turn the key to start the engine and hear that loud metal-2-metal clunk.
Any thoughts?
Is the starter pinion and flywheel missing each other?
-- a clue at 7:20
https://youtu.be/h4Sa8MlOoQ4?t=10m








