Okay there are two breathy noises ferrets make.  One is a "he-he" sound
when they are excited.  Another is an actual hiss.  I have wavs of both
sounds at:
http://www.geocities.com/wolfysluv/wm.html
that one has some hissing on it
 
Hissing can be used as a "back off" kinda of sound that most ferrets never
back up with any overt actions.  Some ferrets do it while they play and
are excited.
 
http://www.geocities.com/wolfysluv/allergies.html
At the bottom of this page, there is a button to push to hear one of my
ferrets doing the "hehe" asthmatic/darth vader thing, ... which is kinda
like the way ferret "laughs".
 
Wolfy
 
Please visit:
http://www.geocities.com/wolfysluv/
for information on ferret deafness:
http://www.geocities.com/wolfysluv/deaf.html
[Posted in FML issue 3636]