I don't get any buzzing at all. I do get a little white noise for a second or 2 out of the audio system whenever I tap the screen. The noise comes from the speaker or the headphones. It doesn't matter what position the volume is in.

My best guess is it is just noise from the audio system and you don't hear it all the time because the power saver shuts down the audio system when it is not in use. Completely normal.