One will hear trains honk even if that train is on a different surface than the player is currently on. This is quite easy to reproduce:

1. Create a short loop that makes the train honk a lot
2. Use the map editor to create a new surface and transport to it
3. You will still hear the trains honking on the other surface

I would have fixed this myself and submitted a pull request, but this mod doesn't appear to have a repository...

Thanks for your time!

I'm also looking for this fix if you have it can you share? Thanks

Sorry for the slow update, I've been unwell. It should be fixed now.