Hi
You need first to get FS Sound Studio
For Starters
Study a Sound.cfg this can be found in your aircraft sound folder, open it up with note pad, you will then see all of the parameters that make the aircraft produce the sounds!
in the viewpoints line it either says
viewpoint=1 or
viewpoint=2
1 is for the sound to be heard inside the cockpit and 2 to be heard outside, there are many other settings that are made within the cfg.
Read about the sounds in MS SDK
Regards Alan