I feel a little bit co-guilty that this "static issue" and the thing I've noticed have probably been mixed up.
What I mentioned was this prickling in the fingertips and a multimeter showing a little electric voltage between
a. grounding and RCA, which is kinda normal. The reason why even with no audible impact the correct phase is important for me and is checked for every new item in my chain and
b. a little, but measurable voltage between grounding and housing of the amp, which is for me a stopper and was the reason to give it back and let my contact decide what to do. Especially when it comes to 230 V in a metal case. Even an eventually pre-production item should not show this.
No idea if this was singular with my sample. No idea if it is reasoned by the dedicated German power net. No idea if it was reasoned by our home power installation, what I can not imagine. But I highly recommend a look on it by the consumers and by the manufacturers. This is my definitive last statement regarding this point. The two last things I want is blaming WiiM and/or getting between fronts.