We've finally completed the patch for the exterior sounds bug on the GP9.
After seemingly endless times of looking in the wrong files, I think I have found the culprit for the missing sounds. I've assembled a small patch file in RWP format for those that would like to give it a try right away -- a "proper" patch (same content but self-installing) is coming shortly for those who don't like the package manager.
You can download the patch rwp here: http://vnhrr.golden-age-rails.com/files/VNHRR_SpringfieldLine-2-0_patch1.rwp
Please let us know if there are other or new issues after installing the patch.