Singing Lady Outside My Window.

A few months ago my husband had just come back from deployment and had a few weeks off, our roommates were on vacation and it was just he and I at our house. Sometime during the day I took an aderall pill and had trouble sleeping when it came time for bed, my husband fell asleep as soon as his head hit the pillow. We had gone to bed around midnight or a little later and I was laying in bed playing on my phone. A few hours later, about 5am, I hear someone humming a song outside my window! It was really faint at first but it got louder and more clear as if it was getting closer and it sounded like a lady. It went on for a while, long enough for the tune to get stuck in my head... I was almost paralyzed with fear and my first thought was to hide my phone under my sheets so they couldn't see the light from it and know that I was awake. At first I thought it might be my neighbors since they usually leave for work a little before 6am but I normally hear their footsteps to the car, the car door open, and the engine start.. after the humming stopped I somehow got the courage to peek outside my window and it was still pitch black out and of course there was absolutely nothing there! Trying to fall asleep after that was a challenge because I couldn't get the tune out of my head.. so now of course I am terrified to be by my window at night.