I had a job as a parking attendant once, and I wouldn't finish work until around 12:30-1:30am. Nothing unusual would happen at work. Instead it would happen on my drive home.
I would be pretty tired by the time my shift was over. I needed to find different things to keep my mind active so I wouldn't fall asleep as I drove. Most times I would turn on the radio and sing a bit wildly. There was one time that I actually had backup.
I was cruising along singing a song called Santeria, by Sublime. I was getting pretty into it and as I came upon the chorus I heard, from my back seat, an extra pair of vocals. It creeped me out but I didn't turn around, I just sat quietly waiting for the voice to start again. Nothing. Thinking it was my imagination I started singing again. "What I really want to know, my baby..." To my surprise, the other voice sang again too!
This time I sang a bit longer, making like I didn't hear it. I then stopped real abrupt in the middle of some lyrics. The voice continued on for another line all by its self. This time I knew it wasn't my imagination, and someone must have been in the car with me. I slowed down to a stop, turned on my cabin lights, and peered behind my seat. No one was there.
For the rest of the drive home I was completely awake and silent. I had no idea what had just happened or how to explain it.
My first experience with something inside my car with me but not my first experience with phantom voices.
Any other people had this occur to you?