The reason why inductors produce whistles is usually related to magnetic field changes and vibration. Here are some of the main factors that can cause an inductor to roar:

1. Magnetic saturation and magnetic field oscillation
    Inductors work by storing and releasing energy through magnetic fields. When an electric current flows through the inductor, it creates a magnetic field. If the current changes quickly, the magnetic field in the inductor will also change greatly. If the design of the inductor is not ideal, or the working conditions make the magnetic flux density too high, it may cause the inductor to enter the magnetic saturation state. Magnetic saturation causes a sharp change in the magnetic field, which in turn produces vibrations that are sometimes transmitted in the form of sound waves, creating whistles.

2. High frequency oscillation of current frequency
    When inductors are used in high frequency circuits such as switching power supplies, the frequency of the current may be higher. The metal wires and the iron core inside the inductor (especially the iron core inductor) will produce small mechanical vibrations under the action of high frequency current. This mechanical vibration causes the housing or structural components of the inductor to resonate, which in turn produces a noise (whistling). Especially when the current waveform changes rapidly, this phenomenon is more obvious.

3. Small vibration of the core material
    Iron core materials play an important role in inductors, especially those using ferromagnetic materials (such as silicon steel sheet, ferrite, etc.) as inductors. These materials are subject to strong magnetic field changes when a high frequency current passes through them. Tiny vibrations in the core can be due to the rearrangement of magnetic domains in the material, or magnetic field vibrations due to rapid changes in magnetic flux. These tiny mechanical vibrations usually produce sound waves, creating an inductive whistle.

4. The design of inductance
    Some inductors may not be designed with sufficient consideration for the effects of electromagnetic interference (EMI) and structural resonance. For example, the housing of the inductor may not be strong enough, or the layout of the iron core and wire winding is not reasonable, which may cause the inductor to produce mechanical vibrations when it is working, and these vibrations can cause resonance phenomena at a certain frequency, resulting in whistling.

5. Work environment factors
    The operating environment of inductors also has a certain influence on the generation of whistles. For example, if the inductor operates in an environment of high temperature or humidity, the properties of the material may change, affecting the stability of the magnetic field or triggering unstable mechanical vibrations. In addition, the load current change of the inductor will also affect its performance, when the load current fluctuation is large, the inductor may produce more noise.

6. High-frequency switching noise
    In some switching power supply circuits, especially PWM (pulse width modulation) modulation and high frequency switches, the inductor is subjected to rapidly changing currents, which can cause the inductor to resonate near the switching frequency, further causing whistling. This noise not only comes from the inductor itself, but may also interact with other components in the circuit.

7. Measures to reduce whistling
    • Use suitable core materials: Choose low-loss, low-noise core materials, such as ferrite materials or low-magnetic loss silicon steel sheet materials.
    • Optimize the inductor structure: ensure that the enclosure and core of the inductor are stable to avoid mechanical resonance caused by an unstable structure.
    • Increase sound insulation measures: Install sound-absorbing materials or soundproof enclosures near the inductors to reduce the spread of noise.
    • Avoid working in the magnetic saturation region: By choosing the working range of the inductor reasonably, avoid the inductor entering the magnetic saturation region to reduce the possibility of noise.
    • Improve the current waveform: Smooth current waveform is used to reduce the sudden change of current and reduce the speed of magnetic field change.

conclusion
    Inductance whistles are usually caused by a change in the frequency of the current, a change in the magnetic field, mechanical vibration, or resonance. After understanding these reasons, the noise generation can be reduced by improving the design, selecting the appropriate material or adjusting the current characteristics, so as to improve the stability and reliability of the circuit.