My roommate and I moved into an apartment complex around Thanksgiving of last year. I had stressed the importance of getting a 2nd story unit as I had heard reviews saying that the insulation between floors was awful. Unfortunately due to improper communication on the managements front we were stuck into a first floor unit. And it is as every bit bad as the reviews stated.

The first few nights of being there our upstairs neighbors would have their young child up and running around the unit until around 2-3am in the morning. Every footfall sounded like a hammer on our ceiling. I tried using my fan on a higher setting and putting in ear-plugs to dampen the noise. And unfortunately, it didn't do anything. I would just have to wait out the noise to go to sleep. 

I wanted to give our neighbors the benefit of a doubt, in that they probably had no idea how poorly insulated the units were. At this point, it was nearing the holidays so I had bought some cards and candy and thought to write them a friendly note. I delivered it to their door with some candies before work. It read like this:
"Dear upstairs neighbors,

I don't know if you're aware of this, but unfortunately, our building's floors and ceilings are not well sound-proofed. For the most part, everything has been okay. However, there have been quite a few times where we have been disturbed and interupted while sleeping from the little tyke running and playing into the wee hours of the morning. We would appreciate if you would please take this into account.
If you have any questions or concerns we wouldn't mind meeting, We'd also like the chance to get to know you better😊!"

The next few nights had been hit or miss, but enough that I thought they were trying. A week or so passes and I step outside and see someone had left their stroller next to the stairs of our connected units. It was pretty cold and wet out, and thought it would be frustrating for the owner to come out to a frozen or at the very least, soaked stroller. I felt incredibly nervous to but I walked up the stairs to see if it was theirs. I knocked on the door a couple of times to no answer. As I was headed back out to the parking lot I heard someone open a door. It was one of the neighbors. I stopped to say hello and mentioned why I had knocked on the door.  Once she figured out I was the neighbor underneath her unit she admitted that things could get loud since her husband came home late from work and that her child was up and down all night. I exclaimed that I really appreciated what they were doing and understood that young children could be up and down all night and that it was probably more the poor sound-proofing than anything. 
Not even two days later, I'm ringing customers out at work and lo and behold my neighbors come through my line. I didn't even realize it until the woman recognized me. She made a point to emphasize that they had left their daughter at home, which I thought was odd. Once she had been cashed out her husband walks over and asks if I was the one who wrote the note. I said I was. to which he asked me again a couple more times, slightly more aggressively each time. The Woman asked me if I had children in a way that made me unsure if she meant
"We heard strange noises from your apartment that sounded like cihldren."
				or
"How dare you judge us and tell us what to do since we have children and you don't"
At the time I read it as the first and told them that I had a cat that occasionally knocked things over to get attention during the day and had a high pitched meow.
But to the second more likely interpretation, I have no intent on judging them for having children. I just wanted to let them know what could be heard from downstairs, in as polite a way as possible.
They had a pretty loud argument that night and its taken a couple more talks since then to get the noise settled down by midnight.
TL;DR:  AITA for asking our neighbors to quiet down?
