Types of Ballast

• Ballast is either electromagnetic or electronic. Older electromagnetic ballast has an iron core with wire wrapped several times around it; this acts as an inductor, affecting the electrical current passing through it. Electronic ballast is solid-state and uses semiconductors.
  
  

Physical Set-Up

• If you hear buzzing from a fluorescent light, first check the physical structure, ensuring screws are tight and the ballast is in securely.
  
  

Magnetic Effects

• Popular Mechanics notes that buzzing is more likely due the type of ballast. Electromagnetic ballast has a fluctuating magnetic field. Pressure from the fluctuations in the field physically affects the core, "squeezing" it at twice the rate of the current, as Cecil Adams of The Straight Dope puts it. This vacillation creates the buzz.
  
  

New Technology

• Newer ballast is electronic, without the magnetic field, and is thus much quieter.
  
  

General Malfunction

• There is always the chance, no matter what type of ballast you use, that the ballast is simply defective. Increased buzzing is also a sign the ballast is old and may fail soon.