Hard to say over the internet but I will try to explain. If the noise is a distict KNOCK KNOCK and it sounds like it is coming from the bottom of the engine, then it most likely is a rod or main bearing. If it is a TAP TAP noise that sounds like it's coming from the top of the engine, then most likely a valve lifer is failing/failed.
the fact that it goes away when the car is warm, makes me lean towards a bad lifter. Normaly if a bearing is bad and knocking, the noise doesn't go away.
The KNOCK noise will be somewhat hollow sounding and the TAP TAP sound will be more solid. If the KNOCK KNOCK is solid, then a rod or main bearing has most likely failed to the point that a new/reman engine will be needed.
No, clean mass airflow sensor. It's extremely common with 4.3. It's a timing issue. Knock sensor is getting wrong information.
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