FSDT, you will need to research your installer tool after installing the GSX vehicles. In FSX and P3d, the sound files for the AI are still left in the Flight Sim.
There's nothing "wrong" in our installer. Most of the GSX vehicles don't have any sound folder in the first place. SOME of them, which are basically cars, have a SoundAI folder which alias into the Automobile\SoundAi folder, which doesn't call any of the sounds you listed.
The issue is, you are using Prepar3D and, in Prepar3D there's a difference in how sounds are generated for AI, I think they use some kind of "default" sound for AI vehicles that don't have any sound specified for them, as most of the GSX vehicles are, because they use our internal sound engine, and this works normally in FSX.
This is happening ONLY in Prepar3D, in FSX there's no Prop sound covering the original GSX sound, you are noticing this problem only because you are using Prepar3D, but in FSX all GSX sounds can be heard normally as they are supposed to be.
We'll make sure this is will be fixed for the next P3D version, it's nothing we should fix on our side, hopefully we'll have a way to specify that a vehicle without a sound folder should't generate any sounds, like it was in FSX.