Knocking/ ringing noise when going uphill or at load

Hi everyone, I'm driving a 2009 1.3L vvt jimmy with manual gearbox, about 150k on the engine.
when I'm trying to accelerate on all gears (usually 2nd and above) I hear a metallic knocking/ ringing noise that looks like it's coming from the engine area.
The more I push the pedal the louder it gets even if the car doesn't seem to accelerate and they stop once I let go of the paddle and reduce the load on the engine.
AC on also makes it appear more often.
I tried to check exhaust heat shields and none seem to be loose. It used to happen only on very steep hills but now it happens on every load situations.
I do need to replace valve head rubber gasket, it's failing, if that can be the cause.
I have some videos capturing the noise but don't know how to upload them.
 

What grade of fuel are you running? Try a tankful of a higher octane fuel and see if that changes anything.

What you're describing sounds like pre-ignition, also known as pinking & pinging, Incorrect ignition timing is a common cause of pinking under load, so once you've established (by running the higher octane fuel) that it is pinking, you can check the timing to see if it's out.

I'm running 95, not so common to find 98 here but I'll try.
Since this engine has a timing chain and not a belt, how can the timing be off?

Do you have a tow bar fitted? Some after market exhaust systems are incompatible with a tow bar and as the rubber hangers age they can allow contact. Also check the engine and transmission mounts for play and the transfer box too.

No tow bar, and all exhaust and rubber mounts are in good condition.

I think Fordem might be right, it sounds like pre-ignition, under load (acceleration or on a hill) is when you hear it.

Although the timing chain might ot have moved, you might have a faulty cam sensor or a lean mixture, perhaps an air leak.

if it is pre-ignition and you have got to the ‘knocking’ stage it needs sorting fast otherwise you run the risk of damage to the engine.  One way to tell is to pull the spark plugs and look at the colour check them against a guide (search online) if it’s white or the insulation is marked/broken or there is wear to the plug ends it is likely to be over-heating due to a lean mixture or pre-ignition.

Robin

It does feel like detonation or pre ignition.
I tried to clean the MAF sensor- didn't help.
I noticed that when the engine is cold the ringing doesn't show but after few minutes drive when the engine is in working temperature - the ringings are heard even with a slight accelaration attempt.
Any ideas on what to check next?