This is a long entry, so please bear with me. My family has lived in the same house since December 2001 on Mercer Island, WA.
Mercer Island itself has an interesting history: Native Americans in the area refused to spend the night/live on the island due to the belief that it was haunted by evil spirits and sank below Lake Washington at night. They hunted and foraged there during the day though.
The house was built in the late 70s by a man who had to flee the state because, during construction, he cut down a large tree without getting a permit or permission from city hall and in doing so, he destroyed a bald eagles nest along with 2 out of 3 eggs that were in it when they were critically endangered.
The ground floor is essentially the basement. The house is built on a hill so half of the basement is level with the ground and the other half is partially below ground. The 2nd floor is the main living space with the kitchen, living room, dining room, and tv room. The 3rd floor consists of several bedrooms, bathrooms, and an office. The whole house is VERY shoddily built and every time my parents make any sort of improvements, they find about 14 new "WTF?" construction choices and problems. The walls and floor are pretty thin so you can hear most conversations that are a little louder than average and people walking around.
Although there were a small handful of strange occurrences in the house early on, like odd orbs in photos and my sister's fear of the closet in her original bedroom in the submerged part of the basement (she had to move to a room on the 3rd floor), there wasn't anything particularly noteworthy.
Then my sister (middle child, I'm the oldest, and we have a younger sister) was raped while attending university, consequently she developed severe PTSD, made a number of questionable decisions, and things have begun to change since then.
She began dating a heroin addict, she swore up and down that he was clean, and when his parents kicked him out, she claimed it was because they were nuts. So my parents allowed him to move in, shortly afterwards I moved out, and he and my sister moved into my old ground-level bedroom in the basement. Predictably, things got messy and there were fights and drama, he began drinking heavily all day-- I was very happy I moved out when I did.
One weekend, I went home to visit and was staying in my middle sister's old room on the 3rd floor. There's a strange little loft in her room that can only be accessed by a ladder, which you can only reach while standing on top of her bed-- she would often swear something was up there. As I was getting ready to go to sleep, I saw, with my own eyes, a large white orb float down from the loft, stop at about eye height, then turn and exit through the door and go down the hallway. I thought it was just some gunk or something on my eye, but my parents cat was tracking it down the hall. She slept on top me that night and growled menacingly at something twice-- I didn't sleep there ever again.
The second really memorable incident happened a few months later. My youngest sister and I were sitting in the living room which is above the room my sister and her boyfriend were living in (my old room), we were playing with her iPad when we start to hear our sister and her boyfriend fighting. And the angry, loud tones quickly became a full on screaming match. We heard her shout, "Get out, just get the f--- out!" and it got more and more intense until we heard our sister scream and it cut off abruptly. Terrified that this guy had hurt or even killed our sister, my youngest sister and I grabbed the dogs and ran up to her room on the 3rd floor and locked the door. We tried to call our mom multiple times but couldn't get an answer. We eventually worked up the nerve to go check on our other sister and found her completely intact and having no idea what massive fight we were talking about. I was convinced, for a long time, she was lying to stop us from convincing our parents to kick her boyfriend out.
Eventually, said boyfriend was kicked out and wound up flunking out of rehab-- his parents sent him to California to live with his sister after that. My middle sister got in two car accidents after that, one was her fault, the other, barely a month later, was not.
My youngest sister was away at college at the time of the third most memorable incident. I was at home playing with my parents dog in the backyard when there was a massive gust of wind that happened out of nowhere (it wasn't a remotely windy day), it was one of those gusts that's so strong you almost can't breathe. When it subsided, my dad came out of the garage to announce that the power had gone out-- there were about 200 other homes near theirs which were affected. I went back inside and began working on a crochet project since there wasn't much else to do with the power out. I hear my dad booting up the generator he bought after a particularly bad wind storm in 2007 knocked our power out for 6 days. As it's revving up, I start to hear my mom arguing with my sister in the basement. She sounds angry and my sister sounds defensive. It dies down, then I hear my dad start screaming, stuff like "That's it, I'm done! I've had it with her!" and immediately, I think "oh crap, she's crashed another car. They're going to kick her out."
I hear my dad start yelling at my sister who starts crying loudly, I hear the bathroom door in the basement slam shut and things are quiet for a while. I'm terrified there's about to be a massive blow up so I grab the dogs and hide in the TV room. I can faintly hear my dad talking to my sister, he's much calmer and sounds apologetic. A moment later the door to the basement swings open and my dad walks in, totally calm and happily says, "I love that generator." I'm understandably confused, my dad isn't the sort to act unaffected when he's upset. A couple of minutes later, my mom walks in the front door with groceries. I ask her what the huge fight was about and she says she has no idea what I'm talking about, but is concerned my dad and my sister had been fighting. She asks both of them about it and they both have no idea what she's talking about. I try to chalk it up to noises in the house being distorted by the sound of the generator, but I'm not convinced-- what I heard was clear as day.
Those are the major incidents, but there have been a handful of smaller ones:
Once, I heard a dog cry in the middle of the tv room and the dogs and I all immediately looked at the exact same spot, but there was nothing there.
I went into my sister's room in the basement to feed her cat once while she was away and nearly tripped over a crate on her floor. I asked aloud, "where did she even get a crate from?" and I heard a girl laugh softly beside me. I was the only one in the house at the time.
Things have gone missing and appeared in a spot that had been checked numerous times before.
I've been touched and heard a voice say my name or a single word.
It's gotten to the point where, every time I'm there and go to use the bathroom, I feel the need to say out loud, "Leave, I need to use the bathroom." Or "thank you" whenever a lost item reappears inexplicably.
For a long time my parents were dismissive or tried to explain things away when I bring them up, but recently my mom admitted to hearing strange things in the house too.
Not sure what to do with all this, I don't think it's malicious despite some of the incidents being scary. I thought it must be residual because the biggest incidents sounded like family, but some of the other stuff seems to be intelligent, mischievous, and occasionally helpful.