I'm using your mod as a jumping off point to make my own music mod, and noticed a volume property in "ambient-sound" properties; looking at Factorio's lua definitions as I was researching for myself, it seems like it should be within the sound = { } part (if you want volume to work and/or not result in errors (idk if it causes an error, or in verbose logging, etc)):

sound =
{
volume = 0.7,
--This has the 4 underscores for the folder, but for some reason it's turned into bold by the website.
filename = "original-music-hd-reloaded/FactorioHaluzsqua.ogg"
}

Per:
https://lua-api.factorio.com/latest/prototypes/AmbientSound.html
https://lua-api.factorio.com/latest/types/Sound.html