Vehicle sound help?

Hi, so I’m making a game as a school project (not for a grade, i have a bet with my teacher that i could make one) and it has a truck in it. I have a sound mp3 file that i would like to be played when the user goes forward, backward, left, or right (WASD mapping). the control setup is basically the default first person controller asset that comes with unity, with the camera moved so it can see the truck and the cylinder replaced with my truck model. Anyway, i don’t know squat about programming, but i do intend to learn so i was wondering if one of you could write me a code in the comment to put on the FPS controller that will make my sound(its called truck.mp3) to play when the user presses the W,A,S, or D keys. Thanks in advance!!!

This is clearly a duplicate of
http://answers.unity3d.com/questions/180316/vehicle-help.html