I've got 5 female guinea pigs. They occasionally will have spats. Recently this aggression has spiked up from one of my girls. She very suddenly turned and has chased the others round their cage mounting and teeth chattering. I've added more water bottles. Feed in separate places. This has made no difference. The aggression is worse at night and I've had to physically separate the guinea pig who started this from the others. Any advice would be appreciated