Noise can travel in odd ways in apartment buildings, traveling down pipes or ducts or air shafts.

It sounds like you have made attempts to be quieter, and that you are limiting the hours in which this activity takes place. This is what a good neighbor would do.

So, if I were you, this is what I would do. I would go to management. Tell them that the two of you are making every effort to reduce *all* noise coming from your apartment, and are making efforts to reduce noise even more after 10 pm. You are not sure why the complaints are continuing and you are beginning to suspect that at least some of the noise is coming from a different unit. You would like more details given to you about the exact time of the noise, the duration and what type of noise it is. This is, you can explain, the only way you can determine if you need to be even quieter, or the noise is coming from a different apartment or if the downstairs neighbor is being super sensitive about noise from your apartment.

The next time Security shows up at your door, ask them what the specific complaint is (shower noise, sex noise, walking noise, talking noise, etc.), what time the noise was heard and how long it lasted.

Because what you need to do is first, determine where the noise is coming from. If it is another unit, you need to make management aware of that. If it turns out to be you, then you will need to work on reducing noise from your apartment.

If you are the cause of the noise, put down some area rugs, even if you already have wall to wall carpet. Put thick padding under the legs of your bed. Make sure the headboard of the bed doesn't touch the wall. Make sure nothing squeaks or rattles.

Fabric helps to absorb sound, so the more fabric there is in your bedroom, the less noise will escape. So put up curtains, hang a quilt on the wall, add rugs.

And once you have soundproofed things as much as possible, then put the question back on management. You go barefoot in the apartment. You've put down area rugs. You've put padding under the bed legs to muffle any noise. You can't think of anything else to do, so now it is management's turn to suggest things. And maybe to talk to the neighbor about what a normal level of noise in an apartment is.

I hope it turns out that the noise is coming from a different unit. But if it doesn't, then become pro-active. Work with management to do as much as possible to reduce the noise. Once you've done that, you can turn the situation around and start complaining about how the downstairs neighbor is harassing you.

I was in a situation where the security guard was accusing me of making noise even when I was sound asleep. I made a record of the dates and times and sent a registered letter to the landlord complaining about it. I don't know if the guard was fired or quit but shortly thereafter she was gone. You certainly have more patience than I do.

If security knocked on my door in the middle of the night when I had been asleep for hours I would be Livid!! If you have been sleeping then its not you and I would think there has to be some type of law that they can not come knocking on your door in the middle of the nigh..Unless something is really going on. I would file a complaint and I would move!