There's always the possiblity they don't realise they're being a nuisance; in the house I lived a few years ago we had the opposite problem in that we had extremely noise-sensitive neighbours who worked night shifts and thin walls, and they didn't bother to come and tell us that they could hear it and it annoyed them when playstation games were played in the back room or when we talked in the garden of an afternoon. Eventually they told the housing agency, who told us, and we went round and talked to the people next door about it and everything was sorted out in about two seconds. Which it would have been if they'd just asked us the first time they wanted to sleep in the afternoon and could hear us instead of suffering a month of worse and worse irritation.
Just to put the other possibility, and all that. Although from what you've said above the situation sounds a bit different.