Even if the noise stops when an injector Is unplugged, it could still be wrist pin/piston related. You’d be taking the load off that cylinder and the noise may not show itself without a load on it.Do as said above by disabling an injector one by one. If/ when it stops, switch that injector with one that sounds good. If the sound follows the injector, it's bad. If it doesn't, it's that cylinder. I've heard of it once and it was a bad wrist pin.
A wrist pin means you have to remove the piston from the bore and replace the piston and wrist pin and the bushing in the connecting rod. It’s definitey fixable, just a little time consuming.If it is Wrist pin/piston worst case scenario does that mean motor is done?
How does one go about confirming this?
This is why the rest of the suggestion of switching the injector is important. If the noise follows the injector, it's the injector. If it stays in the same cylinder, it's base engine or may not have been that cylinder at all (sometimes just changing the load on the engine will change a sound, but not be directly related to that injector...though I would consider this more rare). If it were mine, I would disconnect injectors as recommended, and move injectors if I found a cylinder that seemed to be the culprit. This is a free test that just requires some time.Even if the noise stops when an injector Is unplugged, it could still be wrist pin/piston related. You’d be taking the load off that cylinder and the noise may not show itself without a load on it.