Pedal snaps at every rotation I have a bicycle that after a some amount of use (at least 3000 kilometres since I bought it from someone else) began having some problem on one of its pedals.
Basically at every single rotation, there is a snap in some place, like if there was a crack inside the pedal. That snap its almost impossible to feel when going low on pressure applied, but reasonably felt when running at normal speed, and feels like something is definitely not right and its going to break when either sprinting or climbing.
The closer to the left the foot is, the less I can notice it, (its the right pedal), what can be the cause?
Is it too dangerous to keep going with it this way? By dangerous I mean, the pedal simply getting lose or something like that and go off the bike.
The weird thing is that its a fully metal platform pedal, like this one:

What is there to break? Aren't these pedals just a shaft and the solid outside of the pedal?
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.