I would not be concerned about little noises as the tubes warm up from being cold. But if it is constant after they are hot, try swapping the tubes around. It could be that the bias is way off. If the same tube is noisy, you should return the tube to where you got it and they should replace it. This is not normal. If they were a matched quad, they should give you a new set. You should also be careful not to burn your ear when it is close to the tubes.
Help with noisy power tube!
Hi-- I have a Jolida 502B and just installed a new quad of Svet 6550c's. When the power is on, I can hear one of the tubes making a faint, constant ringing/buzzing sound (like the sound of a lightbulb when you shake it and the filament vibrates), and I can only hear it if my ear is near the unit. The sound coming out of my speakers is fine, as far as I can tell. Is this something I should worry about? Thanks. d