I wonder if the couple upstairs can tell that their baby is crying. I wonder if they have even woken up from it. I know I can hear it, and I always want to take action when a child is crying, to try and help them. But I feel stuck here, I don't really know them and I don't even know what to do about a baby crying. I think perhaps the key would be to figure out why they are crying, but if it's random that seems like a poor solution.
I know that when people (of any age) cry such that I can notice, my first instinct is to help. Of course, it is hard to tell exactly what one can do to help, but usually a good start is to ask them why or what made them cry, and then be a good listener. Even if you can't do anything about the causes, being able to listen and share that knowledge seems to help.