I think having control has a lot to do with it; even the most beautiful music is "noise" if you can't control when it starts and stops. Unpredictability also plays a part: it suddenly starts at a random time and okay, so your neighbour is playing loud music (or practising their instrument); is this going to be for 5 minutes? 30 minutes? 2 hours? All night?

It's very much a personal thing. My brother once lived above a pub, when I came over the pub was playing music and I asked him if the noise didn't bother him. He asked "what noise?" On the other hand he hates living next to a road, whereas I don't actually mind that so much.

Or another thing: some time ago X11 and Wayland were being discussed on HN and someone asked me if I didn't mind the tearing on X11. I had to find a YouTube video to find out what exactly it looks like. Now that I know what I looks like: yeah, X11 does tear a lot, I guess. But it doesn't bother me in the slightest, whereas other people are very bothered by it. I also watch 720p (and lower!) videos/movies and think it's just fine.

I guess my point is that different people are bothered by different things. Person A saying "it's not that bad" and person B saying "it's driving me up the walls" can both be true and genuine statements.

As for your instrument practice ... I don't have an answer. Details matter: are you practising 30 minutes or 2 hours every day? What instrument do you play? How well insulated is the building? Etc. As for "is it not a racket worth its trouble?", no, I don't think so, not if it's severely affecting your daily quality of life (and again, how much it affects people really depends on the person).