The Prometheus theme could be a sacrificial melody from the Engineers society, which they use occasionally.
They seem to interact with technology in melody like patterns (Prometheus star map scene), which make their background even more interesting. I dont think the majority of the Engineer species is hostile to humans and would welcome them.
Only a small group within them,see us as a threat, which are privileged or have a high authority and bacically guide the whole Engineer species like politicians and big companies do with humanity.