Thanks for all responses.
I've tested the same setup in a friend's house, (supposedly well grounded) when I first notice the 50hz hum. I've check all inputs at the interface (presonus 44VSL), different cables and laptop running on batteries. This setup consist of 2xM5, a SM57 and a Audiotechnica AT2035, only the rode pair has the noticiable hum. Later I checked at my house (not so well grounded) and the hum is gone. The only thing is when I touch the rode mics whith my fingers, there is a static noise (hum plus harmonics, but way softer than the original hum problem).
I think I'm going to return them and buy something else.
Sorry about my English and grammar.
Greatings from Argentina.