When my daughter was 6 months old, we had baby monitors set up from her room on the second floor, (back side of the house,) to two recievers, one in the living room on the bottom floor and front side of the house and the other to the kitchen in the back side of the house. By the kitchen is our dogs room where they sleep at night.
Now, I always heard my baby breathing on the monitors, sometimes a cough, or even some flatulence. It was always easy to verify her sounds. Until one night, I was sitting alone and I just start to hear this very low, rumble. And I'm thinking, maybe it's storming outside. Look outside, weather's clear. By then it had gotten louder, and turned into a full blown growl. Long and just eerie. I wasn't sure exactly what it was but it scared the hell out of me! So I ran upstairs and busted into her room to find her fast asleep.
So my only liable explanation was that it had to be the dogs, although I don't see how the monitor could pick that up so well, when the dogs room is on an extension of the house on the bottom floor. But sure enough, I open the dogs door to find one of the dogs sleeping soundly, while the other one has her nose pushed into a corner of the wall, growling like someone had just stolen her babies or something! The creepiest thing about the whole situation is that she didn't even flinch or acknowledge me standing there! Just stared at the wall and kept growling!!! And they're very nice and friendly dogs. I just backed away slowly, shut the door and walked away. I did not know what to do. And eventually she stopped.
Still to this day, the only time I've ever heard her growl. Why she was doing it? I have no clue. And how i heard it on the monitor? It was just bizarre.