I had something similar happen to me while I lived in Boston. I lived in an old apartment building that was originally built it the late 1800s and my roommate and I had an apartment on the first floor. My room had a door in it that led to the back alley and had a small concrete porch attached to it. The alley was kind of cool because friends could secretly park back there and come through my bedroom instead of having to find parking on the street. Anyways, one night while sleeping I was awoken by a very faint noise. Once I was able to get my bearings and come out of sleeping I realized that what I was hearing was a very soft knocking at the door that led to the alley. This door also had a screen door attached to it so in the summertime we could get some air flowing in. The apartment lacked air conditioning. I laid in bed and just kept listening, the knocking continued and then I heard a woman's voice say, "Is anybody home? Hello?", and then proceed to giggle in between asking. The giggling is what really frightened me. After about twenty minutes of this, the knocking stopped and everything fell quiet again. I got up and left my room because my roommate worked late and was off this night so he was still up playing LoL in the living room. I asked him if he heard any of what just happened and he told me that when he went to the kitchen to get something to drink, he saw a short old lady at my door laughing and knocking. He told me he thought I was asleep so he didn't wake me up since I had to work in the morning. I freaked out a little bit and was hesitant to return to the alley at night ever again. I felt pretty safe in the apartment though, the windows had bars over them and the doors all had two deadbolts on them. Still, it was a creepy experience. I lived in the Brighton neighborhood of Boston. At 1626 Commonwealth Ave if anyone wants to check it out. There is access to the alley behind the building on the far right. If you go back there follow the alley all the way to the end, and the last opening is where the door leading to my room was, underneath a balcony straight on. I no longer live there, I don't even live in Massachusetts anymore. I plan on moving back soon though, love it in Boston!