[Craig Kauffman]

Hi, Bob. I have 2-Diva400s and have run across the same issue more than a couple of times. For me it was a lamp seating issue. Sometimes the buzz (60 cycle hum) is also faintly audible at the ballast. The loudness of the hum will be affected by how loose the lamp is, the amount of dimming, and how close any part of the fixture is to any part of your audio system, and grounding. After transporting reseat the lamps, especially after air transportation or long vehicle trips.