The most annoying sound to the owner will be the late night barking. Barking is simply a loud repeated "bark" that is believed to be used to find others or to warn others. They may use this as part of their mating practices as well. This must be taken into consideration when buying a glider as a pet for the first time. You will find that the "all night" barking can drive you nuts and keep you awake at night. Best thing to do is to put the cage in a separate room away from people. If the barking is still annoying, some find that keeping a small night light near them will decrease the barking.
Temperature and environment seems to have no factor with barking. No one is really sure precisely what it means, but barking is normal and can also be collective. Typically one animal will bark alone, male OR female. I think it is a call saying hello I'm here come to me and not necessarily a mating call. I have noticed that when barking occurs, all the other animals between cages stop and listen as if they are in a trance. This I find interesting. Some may bark back. Perhaps barking is simply singing and they bark when they are happy or content or safe...
One way or another, barking is an advertisement of something and is not usually a stress verbalization.
Barking Barking Two barking Four barking after a storm
CRABBING
Another very common and annoying sound will be crabbing. Crabbing is hard to define, but is not far from how a hamster cries when frightened. It is a repeated screeching that they do when frightened, bothered or provoked.
Here is a glider crabbing while fussing with another in the cage.
Here is a pouch of 20+ sugar gliders crabbing:
CRYING
Babies have a way of audibly identifying themselves to their mother by crying. A single baby's cry is very specific between it and its mother, but there can be a wide variety of patterns and sounds between different babies. An offspring will remember its cry for its entire life and will often verbalize when it meets its parent, especially after long periods of time.
HISSING
Sugar gliders use hissing to talk. This can come in many forms and is often the most quiet or "intimate" of the sounds. It often appears to be used to identify themselves up close. This is most usually a friendly gesture or an "ack and response" sort of communication. Of course it isnt all good all the time as this can sometimes be followed by immediate fighting or establishment of intent and dominance if the animals are not familiar with each other or just dont like what they hear.
There are many variations to hissing including: short and fast hissing long and slow hissing hiss-bark
CLICKING, CHATTERING
Much like hissing, clicking is used in close contact and is most often heard when a sugar glider is fixated on another or a new smell or something else possibly threatening. I have seen alpha males clicking when running around the cage looking for a new occupant or trying to locate occupants in a nearby cage. My newest cage of handovers will click from the pouch probably due to me stirring nearby. You can only wonder what is going on in their mind when doing this but I think of it much like a rattle snake rattling its tail to announce its presence and capability of striking, perhaps maybe a hunting or seeking sound but not from a stealthy stance.
Within a cage, clicking from one will often result in hiss-hiss from another as they announce themselves so that the clicker may not attack them as unknowns.
Clicking
ATTACKING
When you are using a cat teaser toy to play with your sugar glider or also when they attack you through their pouch or attack each other, they always use a short burst attack verbalization while doing this. This is always a part of two gliders fighting but largely gets drown out by constant crabbing.
GRUNTING
Grunting comes in various forms but is usually a slower paced repeating sound. It is most commonly heard when there is a problem pooping which suggests discomfort or pain due to constipation. It is also often heard along with other sounds when a sugar glider is self mutilating. If you hear grunting, there is a problem.
Painful Grunting
NURSING, SHRIEKING, SINGING
When mothers are nursing, their nipples eventually get very tender, sensitive, maybe inflamed, and you will most likely see yours doing some shrieking in response. You can tell by their jerky movements that the nursing is bothering them and they would like nothing more than to have it stopped but they usually just take the annoyance and react by shrieking. Very terse "TSST-TSST-TSST" and probably jerking of the body. This is normal and there really is nothing you can do. This sound has also been referred to "singing", although certainly not a cheery sound as singing implies. Here is a more painful nursing.
In this video of a mother nursing you can see her twisting and jerking most obviously because of the nursing baby attached to the nipple.
SNEEZING
While grooming, sugar gliders will make little light sneezes one after the other. It is thought that they excrete saliva and perhaps a little mucus to work into their coat. If your animal is sneezing without grooming or making louder, wetter sneezing sounds, it could be sick and should see a vet.
Grooming sneeze1 Grooming sneeze2
POPPING
"Popping" is a very faint sound that you can only hear with your ear very close. It is commonly heard through the pouch while sugar gliders are inside slumbering, cleaning or just interacting with each other. It is also heard sometimes while eating; "nom nom nom". It is known as the "Happy sound" and has been referred to as purring. Popping seems to suggest that the animal is content in whatever it is doing.
Popping
OTHER
The animals will additionally squeak, bark and hiss when communicating, playing or fighting and they make many other un-noted sounds while active. Most of their sounds are variations and intensities of the ones listed above and can have meanings that we are not able to perceive.
With how little is known about sugar gliders, it would be helpful to you and others in the community (if you do not mind sharing) if you kept notes regarding the behaviors, noises, and similar topics of your sugar gliders.