Neighbor Wars

There's a new property manager in my apartment complex and she's moved into the apartment below us. This morning she left us a letter letting us know that between the hours of 12 and 3 am, it sounds like we're stomping and performing aerobics in the apartment. Problem being that we are not doing anything abnormal in the apartment. We get home from work between 11:30pm and 12am, have dinner, may sit in front of the fireplace a while, but lay in the bedroom and watch tv for the majority of the night. We only get up to get something to drink, go to the bathroom, that sort of thing. I wish I was doing aerobics, because then I could fix it. "My bad, didn't realize you could hear, I'll stop exercising at 2am." I can't stop living in my apartment, and shouldn't have to be confined to the bed when I get home from work. This is the second time we're having to go through this, we had a battle with the previous downstairs neighbor about noise. It'd be one thing if people were complaining about music, a tv, or something similar. But the noise that we're getting complaints about is just us walking in the apartment. They can't realistically put a restriction on when we can and cannot walk in the apartment. I am so frustrated.