Is it possible that the police could tell you? If you call the office, they should be able to tell you if it's a personal or neighborhood problem. Would that be enough to calm your nerves?
On another note, we had a neighbor that we knew in passing down the street from us. For about a month, there were ambulances there at midnight about once a week. My mom finally got up the nerve to bring over some homemade bread for the family and ask if they were ok. It was slightly embarrassing, but they appreciated the food and told us that their little boy was fine now, but had been having severe asthma attacks before that. So, if baking is your thing, you could try the cautiously honest approach. Because you do sound like you're honestly concerned about them, but this is a different situation.
I do I'm in the minority on this. I guess I just see a difference between honest concern and nosiness.