Rats need to work out their pecking order and I keep in mind:
No blood no foul.
Don't break it up if there's no damage being done, or there are more serious signs, including audible hissing, sideways sidling and somebody going for another's rear end or tail in earnest, as opposed to flipping each other over or going for neck or back. Squeaking in protect is OK. Screaming is not.
If you break it up prematurely, the rat with bad manners being taught a lesson or the less dominent thinks, "Wow--that move really worked! They didn't just submit they disappeared entirely!" and they have to work it out all over again.
I find it helpful to slather necks and butts with real vanilla, and drip a little over the back from above with finger flicks.
It can also help to put a BIG box open on one side, or a BIG igloo in the neutral play area. A small igloo can CAUSE fighting, but a big one can encourage them to get closer!
Good luck!