u/Akrobatrajder

Hi everyone,
My Kia Ceed 1.0 tgdi 2021 has a strange noise, during cold startup and first accelerations. The best way to describe it is a “wet fart” or puffing/brapping sound. The nosie stops after 30 seconds.
The noise seems to come from somewhere around the middle section underneath the car.
We already replaced within warranty:

• the flex pipe / flexible exhaust pipe
• the timing chain

but the noise is still exactly the same.
The car otherwise drives normally and there are no warning lights.
I attached a video with the sound (https://www.youtube.com/watch?v=AZUtrBaMAmk). Any ideas what else could cause this? Has anybody experienced this?
Thank you very much for help.