I was doing a run on Southeastern HIghspeed today and the horn for the Class 395 sounded like this...
Sounds like a War of the Worlds Tripod! The horns on many dlc’s especially the US freight ones are really buggy and cut out completely. What I do when that happens is save the game, quit to main menu and then reload the saved game seems to fix most horn issues I have had but it’s not ideal and like many other bugs they should try fixing a few of them.
^ yeah I thought it was pretty funny. Im not too worried about it since it's only happened a couple of times.