Mhm, USB isn't plugged, and nothing in DAC_OUT-AMP_IN.
When there is no signal from the computer the I/O lights are on. I can press the button numerous times but it does nothing. Only when there's sound being played, then you hear the source switching click, and the I/O turns off. It turns back on when signal stops.
Yep, when nothing is connected, P-H forces I/O so that there won't be white noise played. This was the mute mod.