I would like to suggest the remix of the sound for GWE Class 166 units. Although there are various other types that need their sound fixed, the Turbos had a very distinctive rev up sound on initial pull away which then settled to a rhythmic hum. Sadly this is entirely lacking in game and I doubt it will be fixed for the TSW2 GWE relaunch.
It seems there's no internal sounds for the 166, as the cab's near silent so it'd be good if they added them. It'd be nice if they also made the cab windows functional so we can increase the noise from outside if we wish.