In college I lived near a freeway. At nights, I would hear noises sometimes, and it would wake me from sleep and FREAK me out. 
Sometimes  I would hear quick snippets of conversation... I thought I was going nuts, or that I had a ghost. 
One day I happened to  be leaning over one of my speakers, right as a big-rig drove by and I clearly hear CB talk. Mystery solved. That stuff can happen to the best of us.