Bang on their door and like they woke you up, be real nice about asking them to shut up. I had these stoners that lived in my building last year and their living room was right under my bedroom. At random wee morning hours in the middle of the week they would blast their music which would percolate up through my floor. I would just knock on their door and pretend I was half a sleep and be like, "um, could you turn that down, I'm tryin to sleep." Just real nonchalant about it, and well, they usually turned it down.