Who do you have living with you? If you have a pratical joker in the house you might want to look in that direction too
The situation with the electricity could be some of the wires are crossed or that the basement lights are connected to other light switches throughout the house. The actual integrity of the romex should be fine though unless you're living in a coastal town. You can probably figure this out on your own I would'nt spend 70 dollars an hour on a electrition unless you know you need to.
Tell us more about the walking up and down the stairs at night and more about the BIG NOISE! When you turned the light off.