I have a raspberry pi 2 with the Pi2Design 502DAC Pro, using software volume mixer. When I mute the music either with the mute button or by dropping the volume to zero, I hear loud clicks approximately once a second. (I’m on v2.348). These clicks are not present when music is playing at any other volume level.
Edit: this appears to happen only with mp3 encoded tracks and not with flac encoded tracks. It happens with some but not all web radios (I’m guessing the ones it happens with are mp3 but can’t be sure).