Freaked Out

So, last night was the first night Preston slept in his nursery. He went down at 11 and didn't wake again to eat until 3am! Since it was his first time sleeping more than arms length away, I had the baby monitor up nice and loud and woke up every hour, nervous that I may have missed something while sleeping. But at 3 am, he woke and I went to feed him.
After about 40 minutes of eating, he was ready to settle back down. I put him in his crib, swaddled him up, put the paci in his mouth and went back upstairs.
He was peaceful and quiet when I left but by the time I got upstairs, I could hear him grunting and groaning through the monitor. I got back in bed, hoping he would settle back down on his own. He did this forabout 30 minutes while I lay listening.
Suddenly, I heard a voice, faintly on the monitor reception. I immediately assumed I was picking up a cordless phone frequency and thought nothing of it, other than how annoying it was.
Preston got a little louder...still not crying but grunting a lot. Then I heard the voice say, "Shhhh, Shhhh, it's ok. You're with someone who loves you."
WHAT?! I shot up in bed and woke Jay, telling him what happened and made a mad dash downstairs. When I got to Preston's room, he was silently sleeping, all alone in his room (thank goodness!) and when i listened for the baby monitor again the grunting and calming voice was still happening.....long story short, my monitor was picking up a crystal clear signal from the baby monitor next door and that baby that had been fussing and keeping me awake wasn't even mine!!!
Relieved, I decided to sleep on the couch for the rest of the night and forgo the monitor...but it took me forever to get back to sleep because my adrenaline was through the roof from being so freaked out.