My cats do that because they want attention. Since they sleep during most of the day, they want someone to play with them at night. Cats are very nocturnal! Sometimes they may see a stray cat outside, and want to go after it. Or they're just communicating to it. Before we go to bed I play with them, and tire them out. We also have a before going to bed snack together. I give them a few cat treats each. I also made each of them a spot to sleep in my room. Now when I go to bed one of them follows me and goes to sleep right next to me. The others lay in their special area, or hiding spots. If they do get up, I leave toys out for them to play with, and hide treats around the living room so I don't hear anything.