Ok, I dont know what is this or what I'm doing...
I was making some measurements on a professional audio recorder and I accidentally made contact with the probes of the DMM on the GND connector of the power supply and the metal case of the unit. The DMM was in AC Voltage reading and... it measured 8,5 V AC ??
The thing is repeatable. But if I connect for example a USB cable, it goes to 0V.
So the "thing" is only when the unit is powered from mains and without any cable connected.
If battery powered or some cable connected like USB, it doesn't read any value.
I don't know if it's related, but I think, I tried to slowly horizontally slide my finger on the rear metal slot and I "feel" something, like a little "current", of course only if mains powered, on battery, nothing.
What is this? What measurement is this? Is this unit badly shielded?