Honda City 2007 iDSL 1.3 Camshaft Clank Noise?

I hear a single clank noise every time I start the engine for the first time for that day.

A few history:
The car was newly flushed and changed oiled.

Day after:
While driving on the expressway at 140kph, we suddenly heard the engine clanking, indication says Low Oil Pressure. So I asked the driver to pull over quickly. I checked if there's a leak but none and I'm certain we have slightly more than enough oil.

The driver is new, when I asked his often RPM, he doesn't know. He just don't mind the RPM.

The first mechanic I gone to just listened to what the engine sound is making and said that the camshaft should be inspected and probably repair.

But when I got into another mechanic, he said that the oil filter got clogged and suggested to have a change oil again. So I tried to have a change oil and the noise was gone. He also suggest that the oil pump was not damaged.

The next day:
I started the engine for the first time on that day, and I heard a single clank noise while the engine is starting. I tried to shut the engine and started it again, but the noise does not come up.

Then another day:
The noise came up again, for the first start in the morning…

Any help will be much appreciated:)
Added (1). PS: I think the driver let the car rev at 4k RPM which is why he's driving at 140kph… Leaving the oil pump pumping oil at about 50psi… Sucking all the left residue for 8 years…

Honda City 2007 iDSL 1.3 Camshaft Clank Noise?

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