Welcome to glider parenthood and to the forum.
You were VERY lucky that your gliders did not injure each other being put together without any gradual introduction to each other's scent.
Gliders use a long hiss followed by a short bark to call other gliders - this may be what you are hearing.
The hiss/crabbing may just be your young glider calling out for his former cagemates - which may have been his parents and siblings. He is probably very confused finding himself suddenly living with with a STRANGE (to him) glider.
If they are sleeping together with no issues they will probably be fine together though.
It is recommended that you have both gliders checked by a glider experienced vet for a well check-up and have fecal testing done to make sure that NEITHER has any parasite issues. A follow up fecal testing 30 days after the first is recommended as well because parasites show up in cycles and can be missed with a single test. If EITHER glider tests positive for parasites both gliders will need to be treated since they are already cage mates. (many vets will combine pooh specimens from both glider and do ONE test since all will need treatment anyway.