Some background:
I have two male chinchillas (GriGri and Dyno). I got them from a breeder at 10 weeks old and they are brothers. They are now about 2.2 years old. They have always lived together in a 2 story Critter Nation cage. They have play time nearly everyday at about 9:30 for 10-20 minutes (longer and GriGri will pee on the carpet). They take dust baths on Tues/Thurs/Sun. Their diet is Mazuri pellets, timothy hay, and water. They split one raisin once a week.
GriGri is bigger and fatter than Dyno. He has never been very active or social but does let me hold him for short periods without complaint and gets excited for dust baths and play times.
Dyno is smaller (but the vet said he was normal size and GriGri is the fat one) and adventurous. He doesn't like to be held or scratched but loves to jump/climb on things like boxes and shoulders.
PROBLEM:
In the past 2-3 months, I have caught them fighting on 3 separate occasions in the mornings. I hear angry noises from their room and come into to find them chasing each other (NOT playfully) and the little one (Dyno) has let out patches and patches of fur (ALOT). He usually gets backed into a corner and stays super still like he's terrified. One time I opened the cage and he ran out like he wanted to get away from GriGri in a hurry. After these occasions, I close the door between the 1st and 2nd stories of the cage and separate them for the day. By the end of the day, Dyno seems to be dying to get back to GriGri and they are super friendly towards each other. And then they seem to be ok for a couple weeks.
I can't figure out what is going on. I moved recently so I know they've been stressed but this started before the move/packing process.
I went to a vet for a checkup after the 2nd fight and she said they were both fine (well GriGri's fat). She said I could get them neutered if they were having behavior problems (I think she was referring to them humping each other too much). Is this an option? Why do they suddenly hate each other?
I've never been a pet person but I love them and am trying to make them comfortable and happy. This fighting is just driving me nuts. I don't know what to do about it. Any suggestions?