I noticed a few weeks back that the sound of my Lionel Norfolk Southern Heritage Southern ES44AC #8099 sounded a bit off. Not in the sense that it sounded like the speakers were blown, but that the prime mover sounds were a bit quiet and lacked bass. I also compared with other videos and realized that I might be onto something.
Yesterday I went in to look at what might be causing that, and it turned out the foam gasket around the fuel tank was placed incorrectly on the left and right sides. So I adjusted the gasket yesterday and didn't really notice a difference. I tried adjusting today and did a better job at positioning it. I fired up the unit on my test track, and immediately noticed a significant difference in the start up and prime mover sounds. Even the horn sounds significantly better!
You can compare between the 2 videos to see the difference. First one is before I did the fix, second one is with the fix.
Definately a noticable improvement. More diesel "thrum" in the second video.