We had weird stuff happen when we moved in, but at the time you put that down to just being a new house, like one winter the whole of my bedroom window froze on the inside, real thick with ice, it had icicles hanging off the bottom of the sill. I got a bollocking off my mother who to this day is convinced I'd been running water down the window.
It did this overnight and that was the same night as the first time I had been into the loft, we kept seeing a cat in the house very small with big eyes, everyone kept seeing it but could never find it, and always upstairs.
We also had banging in the loft from day one, but my parents said it was due to old water pipes, though when we did eventually board up there for storage, my father found they were no water pipes in the main loft we had a separate water tank closet.
It got worse after I had friends stay over one night and for space reasons we all slept up in the loft, it was like something out of the Blair Witch project, 6 12 year old kids in a pitch black loft after the lights were off with just torches.
Needles to say it ended in a lot of screaming, tears and two kids getting large welts on their backs, my Parents had to go round the various kids homes to try and explain... That's when it got really weird...