First off, I don't think this is actually an issue, so I'm not concerned about it, just curious.
When I turn on my minibrute, I can hear a very faint high pitched "pwip" noise.
The thing is, it's not out of the audio output!
It is producing an audible sound, which I can hear if I put my ear next to it. It might be coming from towards the upper right quadrant of the controls panel, but I don't know.
What might cause this sort of sound in an electrical circuit that is presumably solid-state?