What is tuktuk noise? Prominent when car's cold

[imhere]

Around 0:22 I rev up the Vitz/Yaris engine, the sound also follows engine revving up.

Then I let it idle and it's prominent again at 0:35.

Please listen: https://streamable.com/z54arx

It's more audible when the car's cold. As you rev up at idle, sound frequency also increases.

The sound either disappears or the intensity reduces a lot when the car's driven and is warm enough. Becomes a bit difficult to hear then.

What could be it?

I've driven around 1500-2000 KM after it started coming up... been okay, haven't noticed issues in drive/power.