Have you seen the apartment? Can you hear the neighbors' activities while you're there? Maybe ask to see it around dinnertime when people are home, and see if you can hear their TV, their kids, their dog barking, etc.

For my sub and I who have only the first floor of his parents house at night while they're asleep, or my apartment which is on the floor above the landlord who hears everything, we have simply learned to be quiet. It drives your creative juices a little to think of activities that are quiet; gags are definitely our best friend.

Or you can just not care, and let them hear you and let them think what they want (just don't have too much screaming or they might call the cops).