Watched this video:

https://www.youtube.com/watch?v=r3PA6mmXsWg&list=WL&index=1&t=428s

Downloaded and install this mod for the 377 sounds:

https://www.trainsimcommunity.com/mods/c3-train-sim-world-2/c20-sounds/i16-class-377-sound-mods

Installed it in this folder:

C:\Program Files (x86)\Steam\steamapps\common\Train Sim World 2\WindowsNoEditor\TS2Prototype\Content\DLC

Now the 377 has much better rail joint sounds! (but only on London Commuter)