Hi Cheater, thanks for your reply. I do not know where the noise comes from, I am not a specialist, but I have had other amplifiers that do not emit any sound, so I feel that something is wrong. The 9B has 5 chassis channels each with its own toroidal transformer. The noise that is maintained when it is turned on is the same type that is heard when it is in the process of turning on for a couple of seconds, but it remains constant and with variations in volume.