noise thru tube pre??

As pointed out, your tube is not microphonic just because you hear something when you tap on the case. If it just rings on its own or it continues to ring after you tap then it is microphonic.

Those who think tube gear is always noisy are sadly misinformed. I have an all tube system with 103dB efficient speakers. You can put your ear up to the speakers and hear very little. All components produce a certain amount of noise, even passive components such as resistors. If the equipment is properly designed then it will not be audible once you back away from the speaker a bit.

Newbee, tubes with some microphonics (if not ridiculous) can add a sense of realism to the soundstage. They can add a slight hall or venue presence that has nothing to do with "glare, grit, grain, etc." Unless the tube is overly microphonic some of the best sounding tubes I have ever had in my system have been slightly microphonic. And speaking of "distortion", that's inherent with tubes and is the very reason many of us prefer the sound of tubes to SS to begin with :)

Fiddler, I think there is a difference between 2nd order distortion and a 'ringing' caused by tube microphonics overlaying the music.

That in minor amounts folks can enjoy an artificial reverb like distortion caused by this ringing I wouldn't deny. Studios regularily add re-verb to the mix to enhance a recording, especially dry studio recordings.

But, folks should know there is a difference and by having microphonic tubes you are allowing a distortion to exist which you have no control over. While some recordings might well sound better, and some systems might well sound better, the obverse is also true. And, if you are playing music or components that have considerable energy in the highs already, you might well find that the minor amount of microphonics added to the mix was enuf to make the sound unpleasant, but if you didn't know why you would blame the recording or your system.

Personally, I avoid microphonic tubes as I want the signal to hit the amp as clean as possible. I've always steered clear of any 'signal enhancers' because over the long haul I've always ended up taking them out of the system even though initially their effect was attractive. Thats strictly my choice. Others can tune their system as they wish.

Thanks alot for all info, it only does it when forced by tapping, so I am not going to be to pressed about it, as always you guys once again teach me new things and I thank you all!

Newbee, the only thing I disagreed with in your first post was the implication that microphonic tubes somehow always sound bad.

Enjoying the effect of a slightly microphonic tube is no different than rolling a Mullard for warmth or a Telefunken for detail. Every tube adds its own particular "signal enhancement". None of them comes with an accuracy meter.

I won't deny that microphonics aren't accurate. But like warm Mullards or super transparent CCAs, every tube adds it's sonic signature one way or another.

I think you hit the nail on the head when you said, "Thats strictly my choice. Others can tune their system as they wish."

That's the real joy of tubes versus solid state, IMHO. Tubes offer so many options for one to tailor the sound of their system until they find the "accuracy" that sounds right to them.