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Does it EVER make the noise when engine is cold?
If so then won't be pinging/knocking, and probably not oil pressure either since cold oil is thicker oil.
If it ONLY occurs after engine is warmed up and when accelerating then it is most likely pinging, pre-ignition.
And yes this can come and go because it is specific to cylinder temps, and could be from hot spots(carbon) but they have to be hot enough and the fuel mix lean enough to get self ignition.
Running a tank of 89 or 91 octane through to see if problem goes away or decreases alot would tell you if this was the noise you are hearing.
If your 2.5L has an EGR system then tube or valve can get partially plugged up so not enough exhaust gases are getting into the intake when accelerating, so cylinders are getting too hot.
Hot Exhaust gases cool the cylinders, yes, odd but true, it reduces NOx emissions but a side benefit is less possibility of pinging on Regular gasoline(87 octane) because cylinders are running cooler
Your oil pressure gauge is actually just an on/off setup
The oil pressure switch on the engine will be open(no ground) when oil pressure is under 6psi, and it will be closed(grounded) when pressure is above 6psi
The dash gauge gets power with key on but with open switch it has no ground, when engine starts and pressure is above 6psi then gauge is grounded so gauge shows whatever resistor setting Ford used, usually shows about 1/4.
And movement of the needle while engine is running is from electrical voltage change, not oil pressure.
But if it does drop to 0 then pressure is under 6psi, and if it gets down to about 4 psi you will get valve train noise.