The first experience I had happened when I was a kid. I can't remember the exact age I was, so I will say that I was between six and eight.
I would sit in my room and read or draw and the house was usually quiet, from what I remember. I would then start to hear a raspy breath, like someone sleeping with their mouth open, yet not snoring, just breathing loudly.
Where I lived we had lots of crows and they will sometimes make that raspy caw, so I just shrugged it off as being a crow in the backyard, as my window was usually open.
One day I realized that the rasping noise was going on for some time and I was starting to get annoyed at the crow. I looked out my window and didn't see a crow. Also, the noise seemed to be coming from inside my room and not from the outside. It was also happening in a steady pattern.
I stood up and walked into my brothers room, which was right next to mine and also had a window that faced out to the backyard. His window was open, so I figured if it was a crow then I'd hear it. When I walked into his room all I heard was silence. And when I walked back into my room I heard the rasping noise.
I freaked out and ran out of my room down stairs yelling "Mommy!" She asked me what was wrong and I told her, so she went up to my room with me and of course the sound was now gone. She told me that if I heard it again to just leave the room if it scared me.
And I continued to take her advice until the rasping noise stopped, which I am not sure when that really was, as one day I realized that I hadn't heard that noise in some time. I would say it was less than a year or so after I got scared from it.