We had a concern about this when we built the duplex so we did install a quatro-wall (4 layers of wall) between the two sides. They are connected between the living rooms and kitchen and not the bedrooms so that you have complete sound privacy in the bedrooms. Sound does travel through the quatro-wall but it is minimum. In two years of having this vacation rental this is only the second time we've even received a comment on it. I think it might be when there is an abnormally loud group in the other side--which is also rare. So in summary, there is a slight risk here (though much less than you would experience in a hotel) of hearing some noise from the "other side" but it is not only rare but like K'Lynn said, is easily drowned out.