These cute marsupials, in so far as I can tell make 4 distinct
noises.  The first is the 'get away from me or I'm gonna bite 
you' noise.  This has been described as sounding similar to a 
miniature chainsaw or electric pencil sharpener.  My friends and 
I have taking to calling this 'crabbing'.   You may hear this 
noise a lot at first, but after a month you will learn what's they 
like and they don't and you may never hear this again (hopefully).   
The second is a happy chirp, which they make when excited or happy.   
The third is a quieter chirp which I have yet to find a purpose
behind (other than simple communication).

The fourth noise is a loud sharp barking.  I believe this is some
sort of call for other sugar gliders or just for attention from human
owners.  Unfortunately, this can be very annoying, in that I've been
woken up more than my fair share by this barking.   There is a .wav 
file of this barking at my glider homepage.  Oddly enough, my male glider
tends to do this more often during the period of a full moon.