Chain doing noises... what to do? I have a city bike with a 3 gear hub on the back.

From some time now, from time to time I hear (I think) the chain clicking/cracking (noise) specially when going up a ramp.

Initially I though it was just missing oil, but after greasing the chain it still does the same noise.

Any tips to solve that?

Extra info: When I hear the noise it seems like the chain jumps in the cog?!?! I am not sure though.
Sounds like your gears need adjusting. How to do so would depend on the type of the gears you have exactly.

But if you're getting the clicking and jumping gears, then your gears are out of index.