This happened recently at my house. I am 13 and I live near Brisbane, QLD.
This happened with 2 friends in my pool.
We were diving underwater, when we heard a short, cut off scream. Suddenly, my 2 friends came up and said "did you scream!?" It wasn't me and I told them that. From then on we went under a few times, and heard something every time. It was really scary!
The first thing was a recurring scream. Sometimes it was faint, sometimes loud. Sometimes short and cut off, sometimes long and wavering. I know it was not my imagination because others could hear it too. And we watched each other. It wasn't any of us, because their mouths were shut and there were no air bubbles when we heard the scream. The filter was off. It couldn't have been the filter anyway because it sounded too human. After that we heard a strange sound. A hissing-growling noise, hard to explain. It sounded like a hiss then it turned into a hiss and a growl at the same time. By then we were all freaking out and agreed to go under and listen one more time.
When we were down there we heard both sounds and jumped out of the pool, so eager to get out of there that we didn't even bother swimming to the steps. It was really scary, and when we were inside, when my friend was getting something from the bathroom. My friend said that she had heard the growl again in the bathroom.
Now am too freaked out swim again, especially alone.
My mum's a former-scientist and doesn't have proof, so she doesn't believe me and my dad isn't sure what to think. I don't know what it is so please help me and offer some advice!