Noise when turning on/off tube amp?


I have an integrated tube amp, Cary SLI 80. For the three years I have had it, there has never been any kind of hum or noise. Now there is a 1 second white noise type reaction 15 seconds after I turn it on, and again 15 seconds after I turn it off. Is this a sign that I need to replace tubes? If so, which set of tubes should I be looking at? Calling on all tube experts! Thanks in advance for your comments.
Ag insider logo xs@2xsnooker14
Always, always, always, turn your pre-amp on prior to the amp(s). Always, always, always, turn your pre-amp off prior to turning off the amp(s).
Regards,
Quincy,

While not questioning the validity of your suggestion, I am wondering about the feasibility of turning on/off the preamp before the power amp when using a tube pre and SS power. For me, my SS monoblocks are ON 24/7 while my tube pre is ON only when needed. So my preamp is always turned on/off after the power amps are ON. I hope I am not damaging my equipment doing it that way.