My sugar glider, Vita, never did that. But if I were you I would locate a vet and take him there as soon as posible. Or call a local vet to see if its a normal noise for a sugar glider to make. Alot of people say its a happy noise but you can never be to sure. People say cats purr when they are happy but truthfully, due to scientific reasearch, cats purr when they have any sort of human interaction. This could be something like that. But like I said to be on the safe side I would ask a vet about it. Hope that helps. And I hope your little buddy will be ok.
Please take this opportunity to find A. a vet you can go to in emergencies and B. a source of expert advice on the internet. Next time it might be an emergency and you need something to turn to beyond deviantArt.
Hmm... I don't have a sugar glider, but my rabbit makes that noise when he's happy/relaxed. Maybe it's the same for a glider? I googled it, and I got this:
"Chattering Gliders chatter when they are excited or very happy about something. It is usually heard when they see you and want attention or is sometimes made after a hiss as a communication of friendliness."