Yup its normal, and it gets worse before it gets better. Once they hit 10-11 weeks they begin their "mounting" (uh, servicing) phase, and your big roo will actually hold the little one down and mount him. The held down roo (or hen) will often find a place to hide their head and stay 'submissive' for a long while even after the 'attack'.
I have found that interferring only makes it worse, as they will do it no matter what, and if you try to keep them apart, it will make the aggresser, even more so. Mine are almost 14 weeks old and I tell you it looks brutal sometimes. Now my Top chicken (ChickenDuck) mounts HIS females and beats the other 2 males if they try to. Everyday there is a battle or two because the other males will try to take over. Chickens are alot like a pack of wolves socially. There are Alphas and there are the 'bottom dwellers' that everyone will gang up on. If you remove an Alpha or a bottom dweller, you are rearranging their pack/flock order and they will fight it out all over again to obtain their possitions. Best I can tell you is to let them work it out. If it gets really bad, use a hose from a distance to break them up. That way, they dont assosiate YOU with breaking up their quarrel. AND it keeps you from getting scarred in your "rescue" efforts!
Oh, and the 'scream' you hear is more of a hurt pride thing, not really a pain thing. My theory is no blood, no foul. I only break up a battle if I see it getting bloody. (which has only happened once between the two 'middle' roos)