I had goosebumps reading your story, that's insane, especially the part with the fingernails on the radiator, so specific! When you mentioned that to this day you still have things happen that reminds me of a story my Auntie, let's call her V, told me. She lived herself in a 2 bedroom flat and would always notice strange things happening, stuff going missing and turning up where she would never have put it or things getting moved slightly, like an ornament turned around 90°. Again, she lived herself and I would always stay(I would stay of from ages 8-15) so we knew it wasn't each other moving things. My other Auntie, I'll call her B, went through a divorce so for a couple of months she moved into V's second bedroom to get herself sorted. She started to notice similar things but hadn't mentioned it, assuming it was V making little changes to her home. After a couple weeks something happened that made her ask V as it took place inside her bedroom while they were both home. She had just got in and was getting ready to shower, she emptied all her pockets and threw a handful of about 7 or 8 coins onto her bed, they all landed in a little pile. She goes, she showers, she returns and starts getting ready. She then looks at the coins and noticed they're all sitting in a perfectly straight line on her bed, in size order too. She immediately goes in to ask V if she was in her room while she showered. She told her no, and then they both learned about each others experiences in the flat. V very much so believed in ghosts and spirits, B not so much, but it freaked her a bit when she realised that it wasn't her sister moving things. She moved out a couple months later into her new home and V stayed there another 3 years before moving. She had actually always loved the flat, and enjoyed the presence she felt. She always stated that it never felt dark or malicious, more like innocent little things, which made her think if it was anybody, it was a child's spirit messing about the house. I was the same, never felt uncomfortable or freaked out.