My males very rarely ever croak, the odd time if they sense me in the room or I disturb there tank or if I do heavy mist and they are above ground one will croak which will usually set the off almost as if there having a conversation. And there probably saying something down the lines like this guy is annoying or could he make any more commotion I wish he would just leave. But one will always start then the other will chime in. Maybe this is what is happening with yours if you haven't actually witnessed it. Maybe the one that you think is female if its male never felt the need to sound off, and now that you have definitely got a male Ornate it is setting the other one off and its actually both. Just another thought.