A lot of people have been complaining about the Acer S3 fan noise. This laptop has a loud fan even while doing the simplest of tasks. One forum user on the Acer community forum wrote the below fix to this problem and I have yet to try it on my Acer S3. My S3-391 out of nowhere started running the fan at 100% even if it was cold.
How to fix:
1). Remove the AC power adapter from the laptop 2). Power down 3). Using a thin object such as a paperclip press the battery disconnect switch for 30 seconds. (It is located on the bottom near the back with a picture of a small battery next to it) 4). Power up while pressing F2, enter bios and reset everything to default then exit saving changes