When a microwave is turned on and running, even if it's not heating any food, it can make various noises due to several factors:
Fan Noise: Most microwaves have an internal cooling fan that runs continuously to prevent the components from overheating. This fan helps circulate air inside the microwave, keeping the electronic parts cool. The noise from the fan can be audible even when the microwave is not actively cooking.
Magnetron Hum: The magnetron is the component responsible for generating microwaves in the microwave oven. It produces electromagnetic waves that heat the food. The magnetron can emit a low hum while it's operational, which is normal and may be audible even when the microwave is not cooking.
Transformer Noise: Microwaves use a high-voltage transformer to convert standard household voltage to the high voltage required to power the magnetron. Transformers can produce a gentle humming sound as they operate.
Control Panel Sounds: Some microwaves have audible beeps or tones when buttons are pressed or when the cooking cycle starts or finishes. These sounds might be heard even when the microwave is not actively heating food.
Vibration and Resonance: The internal components and the metal housing of the microwave can vibrate and resonate due to electromagnetic fields and other factors, creating additional noises.
In most cases, these noises are considered normal operating sounds and are part of the microwave's standard operation. However, if you notice any sudden or unusual changes in the noise, such as loud grinding, sparking, or popping sounds, it could indicate an issue with the microwave's components or safety features. In such cases, it's essential to turn off the microwave and have it inspected by a qualified technician to ensure it is safe to use.