I've always thought advanced alien species would employ lots of encryption and compression in their communications and it would thus appear to us as white noise.
Radio is incredibly inefficient as a means of communication. Take your favourite radio station: how much of the broadcast power actually ends up hitting a receiving antenna? About of a googleth of it? Perhaps aliens have come to a similar conclusion and found another means of communicating which we have hitherto not discovered. They could be yapping into their sub-ether communicators all around us and we can't hear them.