by JerryC » Sun Jan 24, 2016 8:55 am
Not knowing anything about this particular locomotive, I can only give you non-specific information. The horn sound specifics are located in the particular locomotives Audio/proxybin/proxyxml file. There, you will see a setting for "Horn Start" and "Horn end". The horn sound file is broken into three sections, with the Start and End files overlapping the looping Middle file. Adjusting the overlap of the Start and End will give you a smoother horn or cause gapping.
I am fairly certain that the problem that you describe is a core game bug. I have noticed while mastering my horns that if you set the horn up to blow smoothly from the Mouse handle pull and the spacebar, you will have a gap from the HUD button. One more reason a loathe the childish looking controller.