Can anyone explain what this noise my ferrets are making means?

We introduced a new 4 month old female (Flower) to our 1 year old male (Sid) today, and they get along very well and have enjoyed playing with each other, but they both keep making a weird sound. I would explain it as a ‘screech’, or similar to a bird’s squawk. It’s not dooking, all though they have both been doing that too since being introduced, and its not super loud or high pitched like the ‘screaming/squealing’ we’ve seen online. They mostly do it while they’re playing, but they also do it while just hanging around their cage, or while they’re each playing on their own. We’ve heard Sid do it every once in awhile before, while playing with him, but since introducing Flower, it’s super frequent. We haven’t been able to find anything that sounds like it online, so we’re really curious what it means.