Interesting information.
When I tried to add a Behringer mixer to my system the case had a high electrical potential.
My wife was dusting the rack and had a shock from the case.
A neon test screwdriver showed a distinct glow.
This was prior to any ICs being fitted.
I just switched it on to see the usual Behringer light show.
Reversing the 2-pin plug in the mains socket solved the problem.
Behringer mains plugs are 2-pin in Scandinavia.
They are also 90 degree offset so they usually follow a pattern in the multiplug.
This one doesn't.
I wonder whether I should take the mixer back? I haven't even used it yet.
I have never suffered from hum though.