Speaker noise after tube amp shut down

Exactly what kind of noise? Pop cracking fading ocean wave? Usually tubes make their aches and pains in the rear known when full power to the grid is present not de-energized.
Im gonna say for an experiment switch the speaker leads to the opposite channels and see if the noise follows to the the corresponding speaker. Lto R R to L This will eliminate the speaker for starters.

Ed

Noise is like bzzz ing for about 20 sec.
First after powering amp down speaker is quite for about 20-30 sec and after that start like bzzzzz noise for 15-20 sec.
Thank you!

Well, do the speaker lead swap to eliminate the speaker. If the speakers are eliminated then put the leads back to the correct L & R connections and swap the amplifiers input IC's from the preamp now if the sound is still in the same speaker we have determined it to definitely be an amplifier issue and im gonna say a cap is acting up.

For now I would let the symptoms develop and become more pronounced because I may not rule out a tube completely as a failing tube has a way of playing havoc on other components such as caps,
Go through your tubes with a tester for starters but thats usually a long shot

What kind of power output tubes are we talking about?

I did't swap speaker cables yet but I will tonight. Right now I'm not home.
Power tubes are KT88, NOS Genelex Gold Lions.
I will let you know how swaping going.
Thank you!

Got a spare set of tubes? How old are the tubes? When was the last time you replaced them? After swapping the cables, I would try changing all the tubes just to see whether the issue is caused by the tubes or not.

FrankC