Here is something you can try at home. Next time you are charging your mobile phone with your wall wart USB charger, put your ears right up to the charger.
Do you hear a high pitch whine?
I do, and one can hear this from up to 1 meter away. This is a video recording of me trying to capture the noise on my mobile but this is probably not working. At least I do not think I can hear the same hum when playing back this video on my aging notebook computer.
Do not panic if you can not hear this whine, your hearing is fine. This whine may well be connected to the home electrical supply and the same charger that whined can be dead silent when use in somewhere else. The exact cause is still unknown to me at this stage.
This noise is similar to a 50 Hz transformer hum/buzz. Where it differs from a traditional 50 Hz hum is this high frequency will not blend into the background noise. You should still hear it when music is playing (hence why the recording couldn’t pick it up is a surprise for me).
Some other things I’ve noticed about this whine:
- As the device gets to full charge, more often than not the volume of the whine gets louder
- When you power off the charger, the volume of the whine gets louder and louder and pitch goes higher and higher. And then everything fades off
- All my USB chargers exhibit this whine. Seems as they age, the noise gets worse
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