Tube amp noise at start up

[kydave19]

I bought a Fender Tweed Blues Junior IV Ltd Edition brand new a few years ago. Never left the house and rarely played.

Recently fired it up and there was a lot of crackle, then verged on feedback, then went quiet and played normally.

I'm cycling it a few times, letting it cool, the restarting. Can I expect the crackling to diminish with more frequent use?

It is very quiet (as to extraneous noise) and sounds great as soon as the start up trauma passes.

Per suggestions, I have carefully pulled out & reinstalled each tube & I have run all the knobs back & forth multiple times.
More detail. After about 3 - 4 seconds of crackle, a feedback loop starts and crescendos in another 5-10 seconds, then quiet and the amp works normally with no background noise. Any idea on the feedback? I've made sure I had the amp freestanding and not backed up against a wall or corner.

All the above happens with ALL the knobs at usual settings (mid range) OR zero'd out at turn on.