I've so missed the railwaves clickety-clack sound drom MSTS. Now I've finally got it :)
If you want it too, you have three options, it depends on which DLC you have. In my collection I have three engines with the right kind of sound, the class 101, 33 and the HSC version of the F7.
the files you need from either of these assets is the BG_Modern.proxybin & BG_Modern.proxyxml (do a windows search to find them)
copy these and replace the ones for the engine you want to have the new clickety-clack sounds. (backup the originals first)
eg:
from: Assets\RSC\Class33Pack01\Audio\RailVehicles\Bogies\BG_Modern.proxybin (and the proxyxml)
to: Assets\Kuju\RailSimulator\Audio\RailNetwork\Bogies\BG_Modern.proxybin
copying to the kuju folder will affect all the stock diesel and electric locos!!!!
That's all there is to it
If you cant hear the new sounds from the cab, then you need RW_Tools to edit the OCCLUSION.BIN file for the affected loco
eg:
Assets\Kuju\RailSimulator\Audio\RailVehicles\Diesel\Class 55\Cab\Class 55 Cab Occlusion.bin
change the value from -1800 to -2400
note - this will increase the volume of most other cab sounds too.
The class33 has the best sounds I think, but they are still hard to hear until you get upto 25mph or more.
hope this helps :)

