What the hell does it sound like when tubes rattle?
I used to have a killer SOVTEK amp but I think I traded it in on a new MESA.
Probably depends on the tube, but it sounds like a high frequency jingling or ringing sound when I've heard it on any of my amps. One of the most annoying guitar-related noises ever. Absolutely kills any possibility of getting a decent recording, but I can't stand it even playing live.
What creates it is a poorly constructed tube whose internal parts are sympathetically vibrating against the glass envelope at certain frequencies. With most new-manufacture tubes, part of the problem is the low quality mica spacers inside the tube, part of the problem is that the haphazard construction of many current tubes results in the metal parts in the tubes leaning to one side of the tube or the other. Though those parts can rattle, too, if the tube isn't well made.
My experience with the Telefunken/JJs has been a 'no rattle' pleasure.
It's more likely with combos than heads, due to the tubes hanging right next to speakers. A separate cab and head isolate the tubes a lot more, though there have been times I've gotten tube rattle even with a separate cab and head.
I was able to solve the rattle on my old set of Mesa tubes with Eurotubes damping rings, but the tubes failed in a short time regardless, something I find quite common with current production tubes, without damping rings.
Interestingly, I've never had a JJ tube go bad in the past. So there's that. Problem is, I don't know if the stock JJs would rattle in my Lone Star or not, so there are no guarantees to this stuff.
The Telefunkens don't rattle, they sound good, and I'm delighted with them.