Yah many times..It does sound like a tube at the end of its life...Sometimes it sounds like bacon in the frying pan!Try fliping left and right tubes and see if the noise travels with the tubes..More than likely you will be buying tubes soon............
Whirring, whistling sound from left speaker
When I turn on my preamp and amps, but with the preamp in mute mode, I hear a whirring, almost whistling-like sound from the left speaker for about 1 to 2 minutes. This happens whether I have a power conditioner connected to the amps or not. I have independant circuits in the house for the system. Both the preamp and monoblock amps are tubed. Any ideas why this is happening and whether it is something I should worry about?