Slight Tube 'Whistle' - Help?

Yes, a circuit can be "hard on tubes" by running them toward the upper end of their designed voltage limits. Or, an off-kilter component elsewhere in the circuit can stress tubes. (I had a CJ tube preamp a few years back that developed a whistle when a power supply capacitor began failing.)

You didn't give the make/model of your preamp, but it might be worth calling the manufacturer and discussing the situation with them. You might want to have it checked.

And it is also not uncommon for tubes to be "microphonic" - some tube types are more sensitive than others. A tube damper can help if you think it is affecting the sound quality of your system.

Your hiss and whistle is commonly called "tube rush," and yes, they do that. Some more than others, some develop more or faster, and at least in my limited experience, preamps appear to be "better" at it that some other tube applications. Trick is to get some tubes in there that work for you, and have extra on hand -- because, sooner or later, the little bastards will start complaining again. And yes, the more sensitive and resolving your equipment, the more pronounced your perceived tube rush will be. When one channel starts to complain before the other -- that again makes perfect sense, as it would be unusual (though not impossible) for both channels to deteriorate at the exact same rate. Expect you should be able to find tubes with a longer shelf life, so to speak, but dealing with this stuff to one degree or another is just part of the care and feeding of tubes. Only permanent fix I am aware of is called "solid state."

As for the microphonics a ringing when you bang on stuff, also perfectly normal and -- as a general rule -- not such a great idea. Don't bang on them. If you've got a tube that is particularly sensitive to microphonics, such that the micro vibrations inherent in the normal operating environment are enough to result in a perceivable sonic degradation, then stuff like isolation or tube dampeners could help. But banging on stuff is orders of magnitude different, and not really helpful or representative. Think about a little kid poking himself in the eye and announcing "but mom, it hurts." Yes, then stop. Not obviously the same with tubes, but when you get right down to it, it pretty much is. Best of luck.

hah!!!! Thanks, Mezmo. Thanks everyone for your help. That was very reassuring. I will monitor...there is nothing but silence right now.

...at some point may try the EAT tube dampers. i already use them in my DAC which is very, very to microphonic problems.

Hi. Thanks the preamp is the new CJ GAT.