Alien energy signals might not have any modulation at all, i.e. they might not have any information encoded. Also, they might be far more powerful than needed for communication.

Beamed solar energy

Sure there are theories describing everything we see in the night sky as just natural phenomena. But, consider the fact that insects do not perceive humans as being responsible for (just about everything we do). Indeed, lower primates probably don't attribute half the things in their environment as human works. It's possible that the 'food chain' extends well above humans. Seriously, there are probably millions of higher hominids that still may evolve from us. Some of these improved humans have already been born.

What keeps us apart from other species is the independence/separation of material resources. As soon as we start competing for the same resources, it becomes a mortal battle. If we really are not at the top of the food chain, all it will take is utilization of the same resources to get the attention of aliens. Like what we do when flies are buzzing around us -- we develop a technology that threatens them (or just irritates them), or if we start into resources that they consider their sole right, they'll swat us. If they exist.