Is the Class D amp prone to electricity? The NAD M33 use class D amp from Purifi, right?But in most (all?) cases of the M33 it is not. I checked for my own unit and another out of the box. If nothing is connected to the unit, a few moments after turning on, the noise starts from the unit itself. Of course on a grounded power supply line.
Many owners of the M33 verified this in this thread and others.