This is something I noticed when I was in the US - It seemed that emergency vehicles leave their sirens on the whole time. Here in Aus they'll leave them off and only turn them on when coming up to an intersection that they don't have traditional right of way on, then back off again (lights on the whole time).

Am I wrong about this? I was only in a couple of cities but it was stark how I could always hear sirens

Where I live it's just like you described in AUS. Policies on this stuff varies city by city.

Ah ok, I didn't realise. I've mostly been within ~5km of Sydney CBD.

Not that strange. Sirens in NYC are largely directional, and you can hear the noise diminish dramatically once you are no longer in the path of the vehicle. The same is not true of loud cars/motorcycles. Also sirens (mostly) serve a necessary purpose for society, while motorcycle noise serve to stroke their owners selfish egos.

I lived in the upper west side 7th fl and sirens are absolutely excessive. Deafeningly loud even in my apartment.

I wonder if the problem is that modern cars are too soundproof. Perhaps they should be regulated to have some kind of transparency mode like with modern headphones so they will hear much quieter sirens.

I hear way more honking than sirens.

But even granting that sirens are louder, they serve an explicit purpose. Loud cars and motorcycles do not.