I recently got a new guinea pig. I was assured it was a male (I think only a few months old). So we brought him home and showed my other male guinea pig. They sniffed each others cheecks (which I told my mom was good). We now have them in the same cage and the guinea pig I had longer is "rumbling" and moving his head from side to side. I need to know if this is a sign of dominance or if my new guinea pig is really a "she" and not a "he".