Hey!

My car:
Ej civic sedan, 1.4l 90hp.
116 000 km
Oil changed a month ago, 5w30
Timing belt replaced 12 000 km ago. (on 104 000 km)

I have had a rattling sound, kind of metallic, coming from the engine bay.
The sound is loud when cold, does not ramp up with rpms, but is vibrating/rattling the most when i rev the engine right past idle.
I cannot hear the sound when the engine has completely warmed up. It fades away when warming up.
I have tried many times to pinpoint where it's coming from, but can never seem to understand.
Maybe the sound is traveling through the engine, idk.
The sound is heard clearest around the valve cover.
The sound can also be heard from inside the car when cold and right above idle.
This might indicate that it is indeed a rattle and not a leak of some sorts?

I have been thinking that is could be a manifold leak as I have read that they can sound very weird.
And it would make sense that the metal expands and closes the hole as it warms up.
But would this make such a loud noise?

Could it be loose valves / bad valve lash?

Any input is appreciated

Things I have tried/checked without luck:
- I have checked with the header heatshield off, sound still persistent
- I have checked heatshields around cat and the rest of the exhaust
- Took the top timing cover off, belt tension felt ok