The answer to 'why is my dimmer switch buzzing noise' is that a buzzing or humming sound from a dimmer switch is a common issue often caused by electrical interference or an incompatible light bulb. This can happen when the dimmer is not properly matched to the type of light fixture or bulb being used.
Some other common causes of a buzzing dimmer switch include loose wiring connections, a faulty dimmer, or a problem with the home's electrical system. In some cases, the buzzing may also be due to the dimmer switch interacting with electronic devices or appliances nearby.