As you can see from the video above, the passenger coaches from the Northern Trans Pennine dlc are making this weird squeaking sound. In the video, it appears that the sound is coming from the couplers or wheels. Not only is this sound really noticable in the coaches, but it also can be heard inside of the locomotive, especially when the throttle is in idle. While not a game-braking bug, its is really annoying and I hope that it can be fixed in the preservation update. Platform: Ps5
Oops. I'll change the thread title. I haven't heard the sound while driving West Somerset stock. That's probably because WSR has 25mph speed limit, and the squeaking can only be heard at higher speeds.