Because of the fan-less design paired with a SSD (as opposed to a spinning hard drive), there is no fan or hard drive to make any noise. The ZenBook UX305 won't make any regular operating noises
The ZenBook UX305 doesn't have a fan, which means you don't need to worry about blocking the vent when using it around pillows and/or blankets. Also, you won't hear the fan ramp up during use because it doesn't exist.
The laptop struggles with heating and performance when used for intensive applications because of the fan-less design of the Intel Core M processor. Heavier tasks require more processing power, which can't be provided without a fan to keep it from overheating.