GUINEA PIG AGGRESSION

Question
I HAVE TWO MALE GUINEA PIGS, BOTH ABOUT 9-12 MONTHS OLD.
THEY WERE BOUGHT TOGETHER FROM THE RSPCA, HAVING BEEN FOUND ABANDONED TOGETHER AND HAVING BEEN KEPT TOGETHER AT THE ANIMAL SHELTER.
ALL THE BOOKS SAY THAT MALE GUINEA PIGS ARE PEACEABLE AND CAUSE NO PROBLEMS.
THIS HAS BEEN TRUE FOR ABOUT THREE MONTHS BUT SUDDENLY, FOR NO APPARENT REASON,THEY HAVE STARTED SHOWING AGGRESSIVE BEHAVIOUR TOWARDS EACH OTHER.
ONE IS A LITTLE SMALLER THAN THE OTHER BUT IT IS USUALLY THE SMALLER ONE WHICH STARTS THE AGGRESSIVE BEHAVIOUR (FACE TO FACE CHALLENGE, TEETH GRINDING, BITING GIVEN THE CHANCE)
IT HAS GOT TO THE STAGE WHERE WE CANNOT SAFELY LEAVE THEM TOGETHER UNATTENDED.
EACH HAS SUFFERED MINOR BITES FROM THE OTHER.
CAN YOU MAKE ANY SUGGESTION AS TO 1) THE CAUSE OF THE AGGRESSIVE BAHAVIOUR AND 2) A SOLUTION.
I HAVE PREVIOUSLY KEPT SINGLE GUINEA PIGS SO HAVE A REASONABLE KNOWLEDGE/EXPERIENCE OF THEM.

Answer
Hi David

I very rarely hear of 2 male pigs getting on then getting aggressive. I am therefore steuggling to give you a reason why this might happen.

All I can say is that if they are hurting each other that you should spearate them.

Sorry I can't be of more assistance.

Andy