Expanding questions about tubes in a preamp

I've had tube preamps that were too noisy for my system's downstream gain structure (both rush noise and microphonic feedback), and no amount of super special tube selection or tube dampers or HRS damper plates or expensive isolation stands did jack about it. Certainly, once you get "Platinum" selected tubes from Upscale Audio, there's not much (if any) improvement to be had from better selection. 

You have to pick a preamp with reasonable gain for your system and good signal to noise ratio. This is one measurement you can glean from Stereophile reviews that actually matters - for example, see the ARC Reference 6's 100dB signal/noise, which is excellent for a tube pre, and tests in my difficult system bear this out.

BTW if your line stage uses 12AX7 and EF86s, those are NOT typical choices for a modern tube line stage. 6SN7, 6922, 6H30 seem to be preferred (also in my experience). Though with the old 6SN7GT types, it is HARD to find quiet examples today.

Gents, how the hell does adding damping rings change the sound of a tube. Nonsense! If your tubes are microphonic (ringing) adding dampers may quiet them down. If you have a noisy tube it won't help. But it also won't hurt. I have never heard anyone complain about, nor have I noticed, a change in sound due to the use of tube damping rings.

Using rubber bands as tube dampers? Sure, go ahead. As long as you don't mind smelling cooking rubber and the bands sticking to your expensive tubes, then cracking and falling off. Rubber bands are not designed to be heat treated.

Next silly suggestion: why not just coat your tubes with a healthy dollop of undercoating? It made my '67 Bug quieter.

... Phew! - this is getting more complicated - may have bitten off more than I can really manage at the moment...

Thanks to all for obviously educated and experienced info.

Hum is either a design or installation fault.
Hiss is a gain structure fault.
Microphonics are a tube fault.

IMO, chassis damping has more effect than tube dampers.

I first used VPI blocks on my Citation II in the late 70’s/early 80’s, whenever they became available. Blew me away. Been collecting more ever since.
Ditto support damping as seen here
http://www.ielogical.com/assets/M-125/VPIBrickDamping.jpg

NO ONE has ever failed to hear the difference!!

@OP - why such a cryptic topic?

As others have shared, there are types of noise that are intrinsic to the component and the tube itself. As geoff points out all tubes have some degree of microphonics and the gain of the component in which the tubes are used has a huge effect on this phenomenon. Placement or isolation of a component also can have positive results. I agree with ieales that damping, isolation or relocation of the component are where you should start. Hiss is usually a component issue. I do not like dampeners for numerous reasons not least of which is mentioned by Ralph at Atmasphere.