I feel sure she is doing this because you did not (in her eyes) pay her enough attention. She is needy and looking for recognition and validation, and when people do not give it to her and make her the centre of their world, she turns nasty.
These are narcissistic traits, unfortunately, to turn against a person in highly unreasonable and manipulative ways when she feels slighted, i.e. that you are not fawning over her the way she would like.
This is the kind of behaviour that can quickly turn malicious and physically harmful, such as scratching your car or sending anonymous notes to the neighbours about you. It begins this way.
She knows that by making complaints to you, she gets validation; you have to respond to it, somehow. This is similar to how a rejected partner can begin to seek revenge for their hurt feelings, their 'narcissistic injury.' She is doing this in part to get at you for being the bad person that you are (in not giving her lots of your time) and in part to get responses and constant contact of some kind.
She would rather have negative contact than not enough contact. So, she is dreaming up drama about which she can complain. Again, the same as a rejected, slighted partner who constantly creates problems out of nowhere, just to get the other person's response.
If I were you, I would begin evidence gathering because this is just the beginning. Write down notes of what she does, and when, times and incidents. Get photos, run CCTV 24/7, keep voice calls, and log everything. Keep a close eye on your car and any external property.
And no, you are not unreasonable; quite the opposite. Everything you are doing is normal living, and it's quiet. It isn't as though you mow your lawn at 3 a.m. And she really cannot hear these things to the level she claims, if even at all.
You have lived there for three years, and only now are these so-called noises disturbing her. It's lies and deviousness.