Sharpening/polishing knives and tools. No music or videos, just the sharpening. Water stone and warm water too.
It’s cathartic to do a good job sharpening and spending the time to get a good result. Especially when you get to the buttery smooth finishing stones. They’re quiet but have, quiet, subtle sounds that are relaxing to listen to.
I think it would be nuclear warfare. Nuclear fission is a universal development for any advanced civilization. It would be easy to construct a nuclear bomb in an advanced civilization. Once a few rogue/pariah states start making them, everyone’s screwed.
Making nukes is easy, the only reason we don’t see more nuclear states on earth is because of the international backlash. With a couple more Iran and North Korea’s we’ll likely meet the filter ourselves.