Chinchillas Fighting or Playing?

I adopted 2 chinchillas from the SPCA about two weeks ago. Both males, one is 3 and the other is 4 years old. They had to be adopted together because they were bonded and the previous owner said they got along very well for the 3 years she had them. They seem to get along well during the day, even sleeping under the same dome, during playtime they mostly ignore one another, never showing any signs of aggression. However, at night I hear them loudly running around their cage as if they are chasing one another and making strange noises that I can best describe as quacking. In the morning I have found hair in the cage. One chinchilla has had spots of hair loss since I adopted them and the vet thinks the other may be chewing his fur because of stress. Are my chinchillas fighting or playing? I am not sure if I should separate them because they have lived together for 3 years. Is this just stress from the transition that will eventually go away or should I look into more permanent separation?