For the most part, sugar gliders tend to be fairly quiet pets. The range of their vocalizations does tend to include a raspy type of bark that is most often evoked at times of fear, stress, or anxiety. When sugar gliders are placed in new environments, when they're around strangers, when they are abruptly handled if they've been asleep and abruptly awakened, you may find that they do vocalize at those times.
We may also find that there are random times where a sugar glider may start calling, barking and vocalizing and there's no explanation and the owner has no idea why it's happening. It is extremely uncommon that a sugar glider vocalizes for no reason or the owner reports a problem, such as excessive vocalizations to the point where it's disturbing to them, but in some instances, sugar gliders will make a vocalization that will just last basically a few seconds and they generally stop once they're aware of their environment. Sometimes when sleeping and startled, a sugar glider may start vocalizing or may erupt with a series of calls that just relate to the anxiety of being picked up and disturbed when asleep.
As I mentioned, it's rarely a problem. Rarely is their vocalization effective enough to cause a noise disturbance. In most cases, it's important communication to indicate some sort of stress, some sort of anxiety, or to alert you as to something that's creating a little bit of stress for your glider. Overall, it's not considered to be a major problem with them.
Although, if your sugar glider is excessively vocalizing or appears to make a lot of barking sound, it's important they have them seen by a veterinarian to make sure there isn't a medical cause for it as well as changes that may need to be made in their captive care where something in the environment may be a source of stress that's upsetting them. If you find that your sugar glider is excessively vocalizing, the best thing to do is try and determine if there's a source for that. It may be something as simple as another household pet walking around the cage, it may have to do with an environment that the sugar glider is living in not providing enough hiding spots.
If they have disturbances in their nocturnal behavior and are awakened or interrupted or upset too much during the day, you may need to amend how you care for and relate to them that way, as some sugar gliders just don't adapt to having their daytime disturbed and it may cause them to be upset every time they are handled, as well as looking for anything else that may be a source of anxiety for them, especially if you hear barking throughout the night. There may be something that they see or hear that's creating a concern for them. So the best thing to do is to evaluate the environment, try to determine if you can identify why they're vocalizing and make any necessary changes to avoid them from having that problem.