I dont know how you can recognize the problem with America, and still have the audacity to say such a bullshit line.
Because you're exaggerating the issue, and the issue with Americans is exaggerating the risks of everything to justify having guns and invading other countries, which actually increase the problems you claim to try and avoid.
Its called common fucking sense. You know how loud you have your music, and you have some basic fucking decency to go "Oh shit" and turn it down.
You don't know how loud it is. Having seen what sort of buildings you guys have, it really doesn't need to be loud to be audible to another apartment. Not everyone is bothered as easily as others. That's why it's important to let the people know.
An anonymous letter in this specific instance would definitely be the first choice. Honestly, what the hell is hacking the BT gonna do? Make them buy a new, possibly even louder speaker? How would they know it doesn't work because someone is annoyed at the level of noise in the morning?
I do it all the time.
Oh and you also read minds, so that you know for a fact that no-one is bothered by you clomping around to music they might hate, but they're not coming to say anything, because they think there's a "statistically significant" chance of getting murdered for doing it?