Hey Ruby,
I had the same thing happen to me when my little girl was an infant. I swear, I even had my headphones on and could hear her crying!!
I think it's sometimes that we hear it so much we become paranoid and end up hearing it when it's not happening.
Either that or we're hearing it when they do it and are having premonitive clairaudience for when they're gonna do it next!
I swear, some of those times, I was right, and should not have been able to hear her!