From what I understand (meaning I've talked to a couple of women and they report the same thing), it's pretty normal to hear babies crying. When there aren't actually any babies crying, I mean.
I'll be in the shower and think I hear the babe wake up from her nap. After I turn off the water, it's clear there's no way I could have heard her over the fan and water from behind a closed door.
We'll be watching TV in the evening and have to mute it and listen. I sneak to the bottom of the stairs and stand there, looking up into the darkness, for no reason.
Compounding this problem is the fact that we live in a duplex and our next door neighbors have a baby that cries all the time. It's hard to tell sometimes which walls the cries are coming through. (The cries are coming from INSIDE THE HOUSE!)
The last four or five days, she's woken up every half hour after going down for the night, needing soothing. I'm really hoping she's working on some big new skill and in a few more days, she'll be back to sleeping a little longer. Cause most of my phantom babies this week have turned out not to be phantom babies at all.