The horn sound as well as the sound of the throttle disappear. I'm driving in silence. Only way to fix this right now is to start the scenario over, but they're long scenarios unfortunately. Please fix. Thanks.
I think you simply need to make the game re-load the locomotive: Go into the free camera and move away from your engine until the pop-up menu for the internal cameras only lists something like default interior camera. Choose that option and you‘ll get a quick loading screen after which sound bugs should be fixed.