Turboshaft engines make no sound
I noticed the new turboshaft engines in 1.7.3 make no sound. If you take a look at the associated part config file, there are no nodes for "Effects" or "Audio" so maybe just copied one of the existing electro-rotary engine part config files that doesn't make any noise?
The part description for the R121 Turboshaft even mentions that it "emits a pleasantly high pitched whine" so I do suspect it is supposed to make noise like the other fuel burning engines.
Also... Shouldn't these gas powered turboshaft engines have alternators? My batteries go dead using these because they don't generate any electricity. Which just seems wrong.
I do acknowledge that the sound of a prop engine may pose a real challenge. As the blades are feathered the sound of the prop should change so you can tell whether or not you're just batting air or have it properly tuned for optimal thrust at altitude and speed. Currently, the only real indication of the blades working well is to turn on and watch the Aeronautical Forces Overlay feature. Aside from memorizing the feathered position (Authority Limiter) of the blades at various speeds and altitude, it would be nice to have some audio clue as to whether or not your props are working efficiently.
Edit: after playing a bit more, and properly mapping power curves with the KAL-1000 I can see that just some simple sound for the engine would be fine. I tune the things for optimal performance now with the KAL, so I don't really need an audio que.