The Mute LED flickers when you play. Is that a problem?

No need to worry. On the V803, the Mute light doubles as a peak-signal indicator. - On MODERN and WARM, it tells you you're reaching the "bottomless limiter," whose action is otherwise pretty subtle apart from holding back breakup. - On QTUBE, the LED flashing should line up with audible breakup. All of this happens in the preamp. After that, the Master sets what percentage of the power amp's headroom you're using, and you'll want that level at or below the rated power of your bass speakers. In short, the flicker isn't a sign of trouble — it's just letting you know when peak signal levels are being reached.