They will also start to mark their territory a lot more. Clean their cages with an enzymatic cleaner, like Natures Miracle or use vinegar and water. Females do not mark nearly as much as the males do. If you are not interested in breeding, get two females, as two males will fight as they get older. Males can be neutered.
Gliders do bark, usually at night.
This is usually a call for attention. Turn on a lamp with a red light bulb in it. This usually helps. It sounds a lot like a small motor shorting out. It means leave me alone or I'll kill you.