Hi, thanks for your reply!
Well I'm using an external 12Vdc-3A power supply and until now, it was connected to a 5vdc regulator (L7805CV) to power the atmega and the rm04 module at the same time. Just now I added another regulator to power them separately and it has improved a lot. Maybe now I'm just being paranoid but I can still sense some blinking. Anyway it's for far as smooth as I wanted.
Now the only issue I can find is that the regulator is really hot (the one connected to the rm04 module). Checking the datasheet the rm04 shouldn't need more than 140mA, and acording to the L7805CV datasheet heat sinking is needed when they have to deliver over 1A output current. Any suggestions powering the module?
Thanks!