I've just recently decided to join this community in hopes of sharing my own experiences, but I have been reading other stories from this site since way back. I have lived in Southern California all my life so far, and I have had a few of what I would believe to be "paranormal" encounters. None are significant - nor that scary - which is why this particular experience "jarred" me.
Not too long ago, I lived in a two-bedroom apartment. I spent some seven or so years within this place before moving out. During this period, I never experienced anything truly "ghostly" and I rarely ever felt any kind of presence (though it was later relayed to us that a previous tenant's relative died in one of the bedrooms - or something to that effect).
Onward. It was late into the night - past midnight - and my father was watching TV. I was also watching TV, but also trying to fall asleep; though unsuccessful. Suddenly, my father - who was beside me at the time - paused the program and seemed startled.
He asked, "What's that noise?"
I soon took notice of the sound to which he was referring. In the small hallway that connected the rooms in our apartment, very small whispers could be heard through the heater's vents (the ones that are built into the walls); not to mention, the hallway door was left open a crack. By the sound of it, it appeared there were two voices speaking to each other - almost as if they were talking about us - but no words could be defined.
After a moment of listening to the voices talking back and forth, my father finally said in a very stern voice, "Who's there?" It was at this moment the voices suddenly stopped.
He continued his program and - despite me being utterly terrified at the time - I do recall falling asleep not long after he finally switched off the TV. (Though I was a bit scared to walk through the hall alone a few days after.) I later tried to consider other possibilities. It could've been the computer, which was sometimes left playing videos at night and I could often hear the audio faintly through the connected headphones. However, I'm certain that the voices were coming from the direction of the hall (and there's no computer there). Also, the fact that the voices stopped almost immediately after they were shouted at and did not persist afterward. (The videos would be on auto-reload and I would have to turn it off myself.)
The incident occurred about a year ago now and I have since experienced nothing else. I am very certain what I heard was not my imagination - nor my father's. I am usually able to dismiss when my mind is playing tricks on me and when something is really "true-to-life" or "genuine". I seek no advice on the matter, otherwise, and only wish to share my experience.
I'm all up for debunking experiences as something normal, but this could be a one time haunting. You say you lived there 7 years? I doubt in all the 7 years you lived there you never heard voices from the vents before. I'm sure the door being cracked open slightly was not the first time in 7 years that it was open so. You probably would have heard the neighbours before talking through the vents and debunked it yourself.
Sometimes spirits just pass through. It doesn't have to be the building or grounds that's haunted.
A medium told me the other day that the whispering we hear is actually white noise the spirits "transmits" (like a radio that's off station), but that we interpret it as voices. Here she's not talking about the audible whispering where you can hear words, but the distant unintelligent whisperings.