I'm sort of new tube amps, I recently got my first one a couple of days ago so forgive my ignorance.

I was playing my tube amp, everything was going fine when at a very specific pitch and tone, when I sustain a chord, I head a very thin glassy rattle coming from the amp.

The amp is a used amp I got from GC and the tubes in this amp are still the original ones they came with, it's a Peavey Valveking 212.

So I open the back up, take out the cage and check the tubes. I tried hitting the tubes very gently with the power on, I didn't have everything turned up though, because I was just scared to. But when I hit the tube, from the tube itself, I heard the exact rattle, like there was tiny metal in the glass that was being shaken a little if I tapped it a little hard. I had the volume on the clean up to about 10 oclock, I didn't really notice any noise from the the amp through the speaker, but that rattle from the tube itself seemed to me almost exactly like the rattle I was hearing while playing.

So, what does that mean? It seems to me that this is the culprit, something inside the tube seems to be causing the noise. Is that normal? Are my tubes going out?
The tubes in there are something from Ruby, which I hear are very cheap and not that great, could it just be that the tubes aren't that good? Would a new pair of decent tubes resolve it?

EDIT: Also, one more thing, whenever I turn the amp off after a little playing, I can hear a very subtle sound of glass sort of cracking very softly. Sort of like the sound of when a car turns off, you can hear things cooling down. Would this be an indication of deteriorating tubes as well?
Last edited by Nikon87 at Apr 17, 2014,
Yup, its time to replace your tubes.
I'm always screwing with my rig. Muh chilluns:
Warmoth NRFR strat JB/Jazz
Mesa Boogie Royal Atlantic, Diezel 2x12
Turbo tuner, J Cantrell wah, Alesis 3630
Green Rhino, Wampler Velvet, Strymon ElCap/Lex, Phase 45
Ruby just rebrand tubes. Some are good, some are bad. Retube it with JJ's.
Popping and farting when it's cooling down or heating up is normal.
Gilchrist custom
Yamaha SBG500
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100

Cathbard Amplification
My band