My brand new Multiplus (not a Multiplus-II) is making a very annoying buzzing sound, even when charging at 5A or less (on the 110v side) - I recorded it here https://www.youtube.com/watch?v=ooxr1Kx_jAk
I have not experienced this with other chargers, and the noise does get louder as the current increases so I suspect at higher currents it will be unbearable.
Some googling and asking around indicates that some MultiPluses do this, but some don't...