EEVBlog #279 why is there audio distortion when alligator probe touches Arduino

[sisal]

Hi

I just watched #279 - How not to blow up your oscilloscope, and noticed an audio distortion whenever Dave touches the floatiung Arduino:
https://youtu.be/xaELqAo4kkQ?t=1191

Why is there an audible audio distortion in an unconnected system?

- Andy

[Brumby]

I take it you mean the faint clicking in the background when the connection is made.  You might notice there is a green LED on the scope that blinks at the same time.

It's not actually completely isolated.  There will be capacitive coupling through the plugpack to the low voltage side.  Connecting the ground lead completes a circuit.