Had the same issue with RTMM sounds being heard. No RTMM Sounds. Quiet at Misty's?? .. Hmmm can't be!.
yet in v3 with the same setup all the sounds were heard. v4 - nada - no RTMM sounds gulls nothing.
Did a few tests late last week and found the following.
My addon setup: All add-ons outside root sim. All xml correct, cfg files, all required files in their respective folders in an external addon directory and folder structure.
Again in this external addon structure, no issue with sounds in v3: ALL RTMM sounds works fine in P3Dv3.
So "almost" a common folder system used between v3 and v4 for all addons): Effects, gauges, scenery/addon scenery, fonts, Simobjects, Sound, etc.. (The "almost" splits/separates aircraft/boats: those that work in v3 only, versus those that work in v4 only. (The ones that work in both are common).
Anyway in v4, once I "moved" the RTMM .wav sound files from addon\sound over to the root sim sound folder, voila sound works. If I move the .wav sound files back to the common sound folder, outside the sim, and pointed to correctly, no RTMM sounds are heard.
(Seems to be only for the RTMM that I can determine so far) but maybe more IE: Tongass has sounds etc. (Might have to move/copy all the wav files from the addon sound folder to the root sim sound folder for sound to be heard in v4.
Now I know my setup was correct and all works in P3Dv3 with all these same files but not in v4 unless the wav files were in the root sound folder. Will play with more next week (as kind of tied up this week).
Norm