My male sugar glider only makes this sound when I'm in bed or out of the room. He's only started making it lately.

https://www.youtube.com/watch?v=-gucXAH5H64

Link didn't seem to work in previous post.

My male made a similar sound after a cage mate died.

My female made a similar sound when I removed her from my sister's pod to my pod.

I think they do it when they are lonely and calling out to their pod mates.

I would need to hear your glider make the sound more to know if it's the exact sound.

This is just an idea. I have no idea if it's correct. My only evidence is that mine made similar noises when they were away from loved ones for a period of time.

We have one aggressive glider in our group, she tends to bully some of the other gliders around, chase them a little, or just hiss and move towards them. That sounds like a quite version of the noise the gliders she is chasing make. But they make it very loud telling her to leave them alone.