I've noticed that when using third-party sound packs the engine (and sometimes horn and bell) audio volume will change drastically from being normal to being muffled to completely muted. I believe this also happens on some dtg and rsc routes so it might be a core issue. I would post a video though the forums dosen't accept large file sizes (thanks dtg).
Might be a thing with the audio files themselves. There have been several changes to how surround and distance works in the game over the years, for the worse. (Such as a train 200m in front and 3m to the left can come entirely from the left ear, because. Also every horn comes from a single ear now.) You could post on Youtube but the real solution would be to record game audio and show the waveform. That's equally informative and also highlights things that the listener might not quite grasp. Even more importantly, it's quick to look at and also saveable. (People won't upload a video to JIRA either.)
Well, you haven't given examples but to make it short: It's not a core issue. It's down to how the audio sources are placed and set up by the dev.
Well, so far i've only encountered issues with searchlight simulations sound packs, though After some testing i've suspected that my monitor's speakers is contributing on top of whatever issues any third-party sound packs have.
I'd say it's probably down to the Attenuation radius set in the sound blueprints. When orbiting with the external camera for example, you notice when you exit the sound source's radius.
