I would imagine it has to do with the fact that the charger is converting ac to dc;perhaps energy loss from the energy being coverted into heat.
Originally Posted by NCHeat
An answer without a question is meaningless.
Information without understanding is useless.
You can lead a horse to water............
I asked a "tech" guy once why a x-former hums.
I was told that it could be out of Phase?
you can get the technical info here
or you probably could just change it out and see if that quiet's it down
Of course I talk to myself
sometimes I need expert advice