Originally Posted by
Al Willits
Found this, maybe it'll help
Humming or buzzing in a fluorescent light fixture is usually caused by a ballast that's poorly built or improperly mounted. The hum occurs as electrical current moves through metal plates in the ballast.
With the power off, open the fixture. The ballast is a metal box about 2 by 3 by 10 inches with wires leading to it. Make sure that the mounting screws are tight. If there are vibration-isolation spacers, check them. Compare this bad fixture to any similar quiet fixtures you may have to identify the problem. It may be necessary to replace the ballast. Also check to make sure that the framing of the fixture is not amplifying the sound. You may need to change the mounting.
Al