Our 2023 gas engine rattles when cold for about 30-60 seconds, we can hear rattle in mornings after tensioner releases chain pressure and it goes away when enough oil press. adjusts.
A clip on tensioner is supposed to keep plunger from retracting, rattle sounds as if we had a diesel, my guess it does not damage eng. if one waits or drives away slow.
Will talk to KIA dealer, may have to leave it overnight, and of course they will want their diagnostic fee.