Mysterious Whispers

I had earlier posted this story "The Stone Cold Figure" where I had mentioned that there were no paranormal activities in my house... But I remember being pestered by a strange whisper. This happened in my bathroom. I think I shall give you a description of the structure of the bathroom. That will help. Its like 1 room divided into two, but there is a wide gap between the dividing-wall and the ceiling; any movement on any bathrooms can be clearly heard from the other bathroom. So it happened like this.

I was in the first bathroom freshening up as because we had guests visiting our house. So as I was washing up my face I heard footsteps on the other bathroom. First I didn't care much about it thinking it to be my sister, but then due to some reason I called out, "who is it?" It didn't say anything. Everything became quiet. I repeated my question. Then this very strange and hoarse whisper answers me by a 'shhhh'. By this time I thought it was my sister trying to freak me out, so I said, "your stupidity isn't going to work on me," in a singsong tone. Then the whisper said "SILENCE." Though it was a whisper it was quite rude and loud and angry. It was then that I understood that it wasn't my sister because she can't carry on with a joke this long. She usually laughs in the end. I could almost feel the anger in that whisper. My sister couldn't really be that furious while joking. She is a terrible actor. It couldn't be mom or dad because they were busy helping the guests. I was not scared... But I was curious... So I said in a ridiculous tone, "who are you?"

It just chuckled and then nothing, nothing at all, I called twice first and then I checked the bathroom,nothing.

I went out and asked everyone if they had been to the bathroom. Even the guests (I know that's a behavior for the shameless, but I couldn't help it, I was curious) I got the same answer from everybody, "no," and yes, there were no children except me and my older sister.

So that's it. I am still curious about that happening and would love to know a logical explanation for that. Thank you