As others have mentioned, it is probably a high pitched noise. You may not be able to hear it, or maybe it is just on the edge and so very hard to judge volume.

As others have mentioned, it is probably a high pitched noise. You may not be able to hear it, or maybe it is just on the edge and so very hard to judge volume. But if you can find a child they will likely be able to tell you if it is switched on or off just by listening. Or one of the many of us who can still hear poor quality LED lightbulbs and TV sets despite the years of hearing abuse. Google coil whine. Be careful with soundproofing, so you don't cause overheat and fire; better to get a replacement charger. Often another unit of the same brand won't have the problem, and you just have a substandard component. Other cases, such as some LED bulbs, you have entire product lines that whine.