Ghosts?

I usually don't believe in ghosts and most supernatural stuff but I found out this morning that I may have experienced something out of the ordinary.

One of our bathrooms has a leak on the ceiling. Sometimes water flows from above like there's another shower head. Sometimes the bathroom stinks. They said there's something wrong with the bathroom of the unit above us. We've been complaining about this forever but maintenance said that they can't do anything because the owner isn't around. In fact, I confirmed with security, no one has been there to visit the unit since December.

Anyway, I constantly hear noises coming from the unit above us. Like someone walking, moving furniture or, when I'm in the bathroom, someone using their bathroom. It didn't bother me much because I thought the people living there were working in a call center and they only have time to clean in the evening or dawn ---- I actually forgot that it was vacant! I only remembered when our helper pointed this out to me this morning. Apparently, she has heard the same noises too.

Scary? A little. Not enough to make us pack up and leave. What do we do? Nothing, I guess. What should we do?