Start off by having a good "shake-rattle-and-roll" of various parts around the engine to make sure there is nothing loose (this can happen with the heat shields on the exhaust, expanding enough when hot to stop rattle?).

Try running a couple of tanks of higher octane fuel (may also blow some of the carbon deposits away too). Note that it takes the ECU a while to adjust to the new fuel, a few days or so.

If it is a definite "engine noise" it could be the oil filter you are using. The Kia needs an oil filter with a non-return valve in it to prevent starvation on start-up from the oil draining back into the sump. If this happens, not only do you not get oil lubricating the surfaces, but you also get no oil going to the hydraulic lash adjusters leading to loud "tappet noise" until they fill again. Try a genuine filter instead of aftermarket.