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.
snooker14
Does the amp, itself, make the noise? Or is it heard through the speakers?
The noise comes from the speakers.
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.
I thought one should always turn off amp prior to turning off preamp. This to prevent any spikes from preamp making their ways to the amp.
WELL! Thanks for the answers, but all of them seem irrelevant to me. How do you turn the amp or the pre-amp on at a different time in an integrated amp? Am I missing something here, or is it you guys? I am sure you guys have answered a very important question for somebody, but I have a different question. Ino sarcasm meant here, but I really do appreciate your trying. You guys were nice enough to respond. Thanks!
WELL! Thanks for the answers, but all of them seem irrelevant to me. How do you turn the amp or the pre-amp on at a different time in an integrated amp? Am I missing something here, or is it you guys? I am sure you guys have answered a very important question for somebody, but I have a different question. No sarcasm meant here, but I really do appreciate your trying. You guys were nice enough to respond. Thanks!
Sorry Snooker14, I need to learn not to read/respond so late at night. Integrated tube amp. (pre-amp and amp controlled by one power switch) does not permit you to perform the recommended on off schedule. Now back to your question. Three years is about the normal life span for a amp tube....you can squeeze a tad more out of pre-amp tubes. They will still work, but the sound quality and sound stage starts to degrade. It is not recommended that you keep a tube rig 'on' all the time. The tubes can be consumed in a few months. Try a new set of tubes for your rig...it's time anyway.
Regards
Snooker14, What power tubes are you using now? What kind of music do you listen? Which you prefer? Oil caps in your SLI80? I ask so that the advise will fit better to your taste and setup.

I use KT88s in my Rocket-88 and have tried JJ Tesla and Svetlana SED(c) logo. I have found the Svetlana softens the top a bit and enhances the midrange with less bottom end compared to the JJs that have a more balanced presentation but can sound bright in the wrong setup. I prefer the Svetlana sonic signature. This is a listener speaking not an expert.
Thanks again for the responses. The tube life is probably near the end as suggested. Funny enough, the noise I referred to has stopped completely, no explanation. I do have oil caps, and will look at different tubes. Thanks again....