What can cause the metal on metal noise on a pull not all the time. on 2004 Ford Explorer

This noise has been there for a year because noone has the same answer. I have been told timing chain, motor bearings and catalytic converter. The sound when they are under it comes from back of motor where the by cat. Converter and manifold and back of motor.

Asked by for the 2004 Ford Explorer
It could be many things, unfortunately and without hearing the noise first hand or being able to do some basic diagnostic tests or be able to drive the car, its hard to say what the source of the noise may be. Could even be a cracked flex plate/flywheel impossible to guess without being able to hear the noise.