This person rarely seems to be an issue at 3.30 in the morning though.
I think we can deduce something from the "always 9am" thing.
Like I get noisy neighbours who don't care are a thing. But also, it's not unreasonable to have a morning routine where you put on some music and do some light exercise at 9am.
Unless its actually blaring to high heaven, I don't see the neighbour being at fault here.
I know it's irritating as fuck, but it's not unreasonable. I used to work nights and still have pretty much the same schedule and I fucking loathe my neighbours, but I have gone there to actually talk to them. These ones can't be reasoned with.