Matt said in the stream that they couldn’t get hold of an appropriate horn for the SD40, so they’re reusing the SPG horn. Until they get hold of one, they’ll update the SD40 to include it, I haven’t heard anything about this since the original stream so if it has already been updated then please let me know.
In the stream IIRC they have the horn audio for the SD40 that will come with Clinchfield in the works, but it won't be there on release, but added in at a later date.
Apparently they do have the raw recording of the correct horn, but it has yet to be mixed and incorporated into the game. This will be a future patch (probably the inevitable new release bug-fix patch which follows in about 2 weeks)
