I recently purchased a Mark V head. It’s my second one. Still don’t know why I sold my first!! Anyway, when Set to channel 2 - Mark 1 mode (normal or bold) I get a horrible equal when I try to set the Treble or Gain to anything past 3:00. Whether EQ is on or off, any wattage setting... No other issues with any channel, setting or feature no matter how dialed in. Any thoughts? Could it be a tube or best to have a tech diagnose?? Any advice or opinions welcome. Thanks.