So other mechanic that repairs only fiats and alfa romeo rold me that belts are manufactured that way these days and should nothing to worry about, unless the sound will start be more "audible" than the rest of the engine or some errors will start pop up or enything else. He sounded like he knows what he is talking about and he told that he did a lot of belt change in that engine. So as i noticed that if car is very cold like today in my place -3 there is no that sound cause rpms are high on iddle but when engine is running hot about 20 minutes of driving this rattling can be heard in cabin if place around is quiet, but turning on air conditioner makes the rpms boost a little bit higher and the sounds is less hearable, so the more pms the less this sound can be heard. Driving or even rolling on neutral there is not even a one rattle. Guess i will just ignore this...