Rather odd that this buzzes only when the lights are on , and only one light. Try this: I have found at times that if the globe is not tightened just right, then each one, or individual ones, will vibrate, sounding like a buzz. DO NOT over tighten the screws which hold the globes on. Actually: Take all the lamps, and globes off of the ceiling fan and check for this noise. The add one globe, and one lamp at the time to see if you can link it to one light fixture. I have even had to rotate the globes, and re-tighten, to get them to stop this buzzing type noise.