I once had 2 males together and they never got to the point of killing eachother. I also had 6 males together and they didn't either. So, it's not a "male" thing always.

Usually if the males (or females) are brought up together, things will go smoothly until the day they die. If they didn't know eachother until they grew up, introductions are needed... proper intros.

Crying can just be the squealing because one rat is pinned. What kind of fighting are they doing? I've witnessed some "fights" (mostly cute and amusing ones) that I thought were going to hurt eachother, but really, it's just one grooming the other a little too hard.. or one has another pinned. Or something similar. Pay close attention to WHAT they're doing when they fight. Do the boys get puffed up? Do their eyes perk up more than usual?

True fighting (usually territorial) is usually shown through puffing up of one's fur.

It could just be them playing around and squealing like mad.