My husband and I moved into our current apartment (a very new building)in June of 2007. For the first few weeks we were there, we couldn't have been happier. We were some of the first in the building and the few neighbors we do have were friendly and polite.
Our apartment, by the way, is on the second story, and is surrounded by other units (above below and to either side).
We left the place vacant for some weeks while we had our wedding and honeymoonen. When we returned from our wedding/honeymoon in mid-July, the upstairs apartment had been rented and people were moving in. We were surprised to notice how loud the process was. Granted, moving furniture is not exactly a quiet act, but it illustrated the thinness of the walls. We were glad that we'd not installed our surround sound system, as we didn't want to distrub our neighbors.
At any rate, the sounds of them moving in have not exactly stopped. They have children who seem to frequently chase each other around the apartment, and we frequently hear loud thuds and bumps at random intervals. Most of the time, we just ignore it, but every so often we're forced to look up and hope no one's been injured, based on the loud percussive nature of some of the sounds.
We have never spoken to them about this, chalking it up to apartment living, and have just borne with it. There is also a LOT of noise when people run up and down the stairs with strollers and such, but again, we understand that life is difficult when you have small children, and try to grin and bear it.
Last night, something very bizarre happened. My husband, his friend (singular) and I were watching a movie. It was about 12:30 AM, so yes, a little late, but the volume was not unreasonable. I'm usually the first person to ask my husband to turn it down, as he likes to watch things louder than I do, and it hurts my ears. At any rate, there is a sudden pounding at the door. I answer it, despite not being able to see who is there (hall lights out of order), to find that it is two police officers.
They peered into our apartment and asked us if the party had just ended, because one of our neighbors had made a noise complaint about our loud party. We were shocked!! I said, "Wow.....really? We've just been watching a movie. I didn't think it was that loud (the movie was still playing at this point), but then again, we're always hearing the upstairs neighbors and their children, so I guess the walls are pretty thin here."
The officer chuckled at this, and told us that the complaint about our "loud party" had actually come from the upstairs neighbors. He then told us not to worry about it, suggested we call the management about the lights being out, and wished us a good evening.
First of all, I am dismayed that our neighbors would call the police without bothering first to speak with us or the landlord. Had they spoken with us, we would probably have turned the movie off altogether to help them out, and certainly would have been very apologetic.
So here is my dilemma: I would like to respond in some way to this situation with my neighbors. Several methods for doing so have come to mind, but I wasn't sure which was the best course of action to take, especially given some of the potential legal repercussions that could result from this situation. Perhaps someone can give me an idea which course(s) would be the best for us to take.
1. Ignore it and go on with our lives, albeit quietly.
2. Inform the rental management of this incident, so they hear the story from our perspective.
3. Write my neighbor a letter of some kind - apologize for the noise, and suggest that they talk to us next time before calling the police.
4. Other ideas?
Thanks so much for your help out there!

