Adjusting in-cab volume levels?

Is this possible to do? Just to name a single example, the ES44AC in the game is far too loud inside, even when idling. Listen in on this cab ride in a UP ES44. The engine is there but it is very muted, and the horn is quite faint. The RW ES44 sounds like a busy machine shop inside by comparison, and it's even louder with custom sounds. A far cry from the modern "comfort cab".
http://www.youtube.com/watch?v=IzDNSLJ2Nz0
I've looked at various files that might have an effect on this and tweaked a few numbers, but it didn't make any difference. If someone could point me in the right direction I will salute you!

http://www.youtube.com/watch?v=IzDNSLJ2Nz0
I've looked at various files that might have an effect on this and tweaked a few numbers, but it didn't make any difference. If someone could point me in the right direction I will salute you!
