The answer to 'lighting installation making buzzing noise' is that a buzzing sound from a light fixture is usually caused by an electrical issue. This can be due to a problem with the wiring, the light bulb, or the fixture itself.
Common causes include loose connections, a faulty ballast or transformer, or a problem with the light bulb. If the buzzing is accompanied by flickering or dimming of the lights, it's likely a more serious electrical issue. In some cases, the buzzing could also be caused by interference from nearby electronics or electrical equipment.