Knock knock. Who's there?

They can appear in different faces with different voices. You can ignore them but they make sure that you know they are there.
This happened when I was 16. I was visiting a relative with my family. We knocked on her door and we heard my aunt calling her son to open the door.
It was so clear that my mom said, "why is she not opening the door?"
In my aunt's house there was a bathroom and it was quite hard to open the bathroom door's lock. So if someone opened its lock, you would hear it and we heard that lock open to which I replied, "maybe she's in the bathroom that's why she's telling her son to open the door." We knocked again and my friend who used to live downstairs came up and said, "my dad called her and she said that they are not home and will be back shortly so here's the key." We looked at each other but decided to ignore it but we knew we were not alone.