Pedal snaps at every rotation
There are bearings inside the pedal that are meant to keep things running smoothly.  If it was just the pedal itself around a metal shaft, then things would probably wear out quite quickly. Some pedals are serviceable, while others are meant to be replaced completely. 

If you are sure that the snaps is coming from inside the pedal, and not from inside the bottom bracket or where the crank arm mounts to the bottom bracket, then it's probably a good idea to just replace the pedals.

New pedals, especially platform pedals, can be obtained quite cheap and can be replaced basic tools you may already have.  If you don't have tools, the bike shop would probably install them for free if you asked nicely.