Hi For some time I have a problem with my amp. After start-up, while the mute button is on, turning the Tube Gain to 0 I hear louder noise like lamps were "burning" but nothing is happening inside the amplifier. The sound stops when I set Tube Gain to 5 or above. Once encountered a situation when playing on instrument, the volume level balanced from 0 to normal sound. Do you know what is the reason? Will replacement the lamps help?