1, the circuit is designed with a switching power supply, in which the switching transformer will make a squeaking noise, which is the sound of the magnetic core is not tight and the oscillation frequency is higher.
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2, is the transformer, will make a sound just have a large and small. The squeak emitted by the high-frequency transformer is not loud and has no effect on the circuit and can be ignored. I hope you found this helpful
Play wireless charging bank, charging when the current sound, because he is conductive charging through the wireless area