Macbook Air makes weird noise on startup and opening lid.

Yesterday i was playing a game on my macbook air and it got very hot and loud so i put my mac to sleep and a couple hours later i woke it up and i just saw a black screen and the charger was plugged in so i knew it was not dead. so i clicked some of the buttons and it would show the mouse curser for a brief second and a black screen behind it. i kept doing this until i found ou if you hold shift control alt and the power button it resets something so i did it (not knowing what it would do). after doing this a couple times it turned on like it always does and from there its been fine. but when ever i turn it on or wake it up it makes a wierd quiet sound like a zipper being pulled up fast but its very quiet and it sounds like it comes from where the headphone and charger plugs are and i really want to know what this noise is in case its serious of not. Thank you