Bad news then , it's really a great tiny system apart for the fan curve that it has. After some time and when the temperature is around 45C the fan goes in this up and down spiral, ramping up and down, up and down... it's driving me crazy! :)) I tried different Bios versions and I had a motherboard swap on warranty but it's still doing the same.
I was hoping that I could record the RPM and open a support ticket with Lenovo but there is no app available currently that is able to show fan RPM, it's easy to show than to explain. Oh well, maybe they will fix it in a future Bios version.
Thanks for the replay.