Underground activities have taken place all over the United States in conjunction with activities desired by the Service-to-Self aliens who early made contact with the government. The government soon became wary of these aliens, and rightfully so, but have not disrupted the agreements they entered into for fear of reprisals. Since these aliens seem more powerful than the government forces, and could presumably do as they wish with the Earth and its inhabitants, the logic goes that there is no harm done. In truth, as the citizens of the United States don't burrow under the Earth but live on the surface, there in fact is no conflict. There are factions of the government who plot means of destroying these underground conclaves of Service-to-Self aliens, who have developed their own hate club, but it is all fantasy and no results.
What are these aliens doing down there, and what future repercussions will this have? They are in fact not occupied in any useful activity at all, but are keeping it up just because it is upsetting people. Their goals, as we have stated, are to gain recruits. Fear and suspicion, rather than cooperation and enlightenment, are their mode. They have taken to emitting low frequency sounds, which some but not all humans can detect. This affect health, and makes everyone uneasy, especially as the government can't explain what's going on and gets the blame. Humans hearing that the government is up to something down there, in conjunction with evil aliens, are discomfited, and that, of course, is the goal. Good, say the Service-to-Self aliens, lets thump around some more down there, and get on everyone's nerves. Soon they'll start suspecting each other, pointing fingers. What fun!