Ah my bad. I was under the impression that it did. Because when i'm using a cargo plane i get cargo containers (For example with the 777F) so i was thinking that something like this could solve it:
Well, thank you for the free programming advice but, of course, we obviously know how to do it, and in fact, the work being done for the Cargo expansion means we already placed some kind of information about the airplane being flagged as cargo or not so in the plane database, and of course, it will play different boarding sounds in that case.
But again, it will all come together with the cargo expansion, no point adding it now, when you already have a workaround explained in the thread I've linked (setting the boarding time close to 0), which will prevent boarding sounds to be played.