I have an old medicine cabinet with fluorescent lights attached and it has an outlet on it. I keep a little 4 watt nightlight plugged in to that outlet, which stays on all night. Two nights ago around 3am, a high pitched noise woke me out of a sound sleep and I traced it to the fixture, turned off the nightlight and it stopped. Last night it started at 2am again. This time, turning off the nightlight didn't do it. I stripped the fixture - lightbulbs, starters and turned off the power switch on the side of the unit and it would not stop. I wanted to flip the breaker, but they aren't marked (100 yr old house)so I didn't want to mess with things. It finally stopped on its' own around an hour later. Do these old units have ballasts, other than the little starters for each lamp? What else could it be?