What is the noise after the fluorescent lamp is turned on?

Fluorescent lamp consists of fluorescent tube, ballast and upconverter. Under normal circumstances, during the start-up of fluorescent lamps, due to the role of bimetal in the upconverter, a "beep" sound will be emitted to start the fluorescent lamps to emit light. There is a noise after lighting, usually the kind of "buzzing" current sound. This kind of noise is caused by loose silicon steel sheets in ballast assembly, poor asphalt impregnation process, and some small factory products omit asphalt impregnation links to reduce costs, which is easy to cause noise in use.