Technically if a noise is able to be heard in another person's house and is causing them 'discomfort' then it is actually offensive, however getting anything done about it in professional avenues would prove difficult.

However, I agree with MD. Not sure how friendly you are with them but there's a mum in there if there are kids and surely she remembers how hard it is with a little person.....but I would go overboard on the 'nice'.