Neighbors dog keeps crying?

or moaning or something.. I live in a duplex and the owner of this place lives on the bottom part of the house. I know for a fact this lady is pet sitting two dogs but anyway one of the dogs keep doing this cry/moaning thing and its kinda getting annoying and its sad to listen to. I don't wanna be that annoying super sensitive neighbor and go over there and be all like you need to shut your dog up but then again i don't want to hear this all day long. What should I do?