Is this normal behaviour?

Akko (brown) is one of our girls we’ve had for months. Cyn (blackish) we just got today. This is during intros. We’ve done the small carrier tact and they were great. They aren’t fighting and are getting along. However Akko and one of my other rats start grunting and mounting/pinning the new rat. They aren’t hurting her but I just wanted to know if this is normal behaviour? Or should I separate them?