some gliders love to crab, I have read some are the alarm system for the colony.
in our 6 glider colony we have one the will always crab when we get the pouch, but will stop when she sees its us.
in our 5 colony, newer gliders, we have 2 or 3 that are still nervous and will crab alot, even after seeing us 1 will still crab and tell us to go away.
they should get used to you someday and to crab unless they are in pouch and you bother them, then you could have 1 the will always crab.
the chomping sounds alittle odd, but should go away with time. my wife's glider is friendly to me, but with our 13 year old he will try to grab his finger and give him a small bit. maybe he is expecting a treat. one of our less bonded gliders will give a small nip if I put my finger in her face and leave it there.
in the end, don't worry about crabbing, like a dog barks, just their protection alarm system.