If an aircraft's sound file aliases to an aircraft that isn't in your 'hangar'
you will hear the default aircraft sound, that is, WHATEVER aircraft you sim STARTS with.
Open the sound folder in Mike Stone's aircraft. The one you like.
It will look something like this
[fltsim]
alias=b737_400\sound\
Copy THAT INFO into the one you want to sound like Mike Stone's.
You mean the Sound.cfg file in the Sound folder. It's actually much easier to use the method I suggested. Paste a copy of the Sound folder into the aircraft you wish to use it.
PS. I checked out the iFDG MD-11 & the sound is aliased to the default b777_300 which is in turn aliased to the B737_400. This is the cause of the problem. I believe there's a separate sound pack available for it.