MultiPlus II - toroidal transformer humming

[alexpescaru]

@Ringmaster

With certain loads, the case was huming like a angry cat, but if I tapped my finger in the center on the case, it made evident that the problem was the vibration of the cover (and the screws were firmly tightened).

Long time ago, I’ve realized that an APC UPS was resonating like hell during load.
The same transformer problem in a steel metal case.
How I solved the problem?
Replacing the front cover with an aluminum one… No more noises and/or vibrations.
The steel cover was interacting with the transformer magnetic field. No interaction with an aluminum cover, aluminum being nonmagnetic.

[Ringmaster (David Losada)]

Good point!! It must be that, as only was happening just over the toroidal transformer.

[usernamepasswordbs (No)]

My two MPII 5000s are not in the house so I don’t really notice the noise but where they are mounted I first screwed a sheet of OSB to the wall. I wasn’t thinking about noise reduction but to make mounting all the other gear and the cable clips easier. It is though a great first step of decoupling without opening up the case of your Multi.