ILoveMacs

It may of happen if you're are using windows based applications, for example I have had fans being on full power when used skype or especially google chrome, I don't know why but this was happening only with one of my Macbook Air. Also maybe you have done data migration from your old mac and that transferred some applications that are not fully supported by the current OS. I would suggest first to search for local mac repair shop and give them to diagnose your device and see what the would advise before returning it back to apple genius bar.