so I live in a single family, attached, multi story dwelling....a townhouse. I am surrounded on either side by other people. We have a total of 32 of these units in our little circle.
When we first moved in, I typed up a note, with my name and email on it, staing that I, and my step son, would be practicing drums sometimes on Saturdays between the hours of noon and 6pm. In the note, I told people to let me know if they worked night shifts (as my wife does), or idf they had babies with sleep schedules etc, and to let me know about it.
Not only did I get positive responses from people thanking me about my concern and honesty, but I also met another drummer, a bass player, and a retired band director living in the same complex, and also made 2 connections for private lessons. And, I got to just meet everyone in our complex as well.
to this day, I have never had an issue with playing my drums in those hours, and I never play outside of those hours on my loud drums.
in your case, it is obviously too late to do this, but it is just an example of a way to handle it if you ever move, or need to change something.
and while I sgree that anonymously dropping of the mutes was sort of passive, I still think that the gesture was more honest than calling the cops anonymously.