If it is not the kevlar belt slipping (check the tension) then I know what is it.
At first the store (an official store) said that everything was fine (WTF?), and they said that after they took the bike for a full WEEK to check the noises.
So I pick up the bike, rode it and the noise came back. 10 minutes later I was turning to the store to have a nice conversation with the “expert” that told me that everything was fine. Guess what? when I came back to the store the “mechanic/expert” was missing so I complained again to someone else.
They ended changing the folding pedals (now I have another ones from Dahon) and the noise is gone.
On the other hand I keep hearing the brakes (disk friction?) if I’m close enough. In this case the same “experts” said that the bike was new and needed more miles (again: WTF is wrong with this people?).