I started making more noise after my neighbors clearly did not realize that the quiet they enjoyed from my apartment was out of deliberate consideration on my part, and not a mutual experience. I started with normal sounds like coughing or laughing or playing some music, but after that didn't work, I started to make noises they would be embarrassed to ask me about. It somewhat worked at reducing their noise levels. I knew they heard me because they stopped making eye contact. But they were also awful people so that was fine with me.
Thankfully they moved and I now have a quiet neighbor who gets to enjoy my silence. Occasionally they'll get a little noise from me to remind them that the wall between my bedroom and their main room is very thin, but I haven't had to escalate it like with the last people, for which I am grateful. My other neighbors are a very quiet elderly couple and I love them, but our shared wall is substantially thicker, which is partly why I love them.