This has now been added to the pause menu. This might move to an on-screen button in future if the mobile view changes, but this allows the sound to be disabled for now :)
Great, thanks for adding that option! I will now put myself to sleep every night watching this while listening to real train sounds :)
Just a heads up: the music does not come back when toggling sound back ON (sound effects do become audible again). Resetting the cart via the menu brings it back. If it matters, I'm using Safari on an iphone, latest ios version.