What causes microphonics ?

I have a Rogue Magnum 99 preamp. Sometimes it exhibits microphonics, and sometimes it doesn't.
I have found this very difficult to eliminate. I have tried numerous amounts and types of different tubes. It still comes and goes. One time I turn it on , and no problems. Next time, it's there.
Also, does this effect the sound ? I would assume it does in some way, but I am not positive.
Thanks, any info would be appreciated.
If a component is microphonic, you can bet your bottom dollar that it is affecting the sonics.

In terms of what is causing this, it could be tube based or something as simple yet complex as an intermittent solder connection. Short of pulling and reseating all of the ( Known good ) tubes and re-flowing all of the existing solder joints, it may be next to impossible to find.

Just think about this though. If you think that it is frustrating, this is the kind of stuff i make my living doing. Needless to say, i have to hide the hammer from myself with some units : ) Sean
Typically, the tube shouldn't be microphonic and if it is than it's bad or bad biased. In untraditionally desinged Rogue equipment it's not a surprise to me.
generally in my experience it is the tubes and, to a lesser extent, capacitors. Capacitance is the culprit. The voltage across a tube or cap depends on the distance between the elements or plates. If these move because they are loose due to vibrations (either you tap it with a finger or vibrations from the music) the voltage accross the elements/plates must change. Since the audio signal is kind of stored as voltage at this point in the stream you must hear the effects of this change.

Some microphones are designed to work in this manner. They are just special capacitors. When you blow/sing on one sensitive "plate" it moves and the distance between the plates changes and creates/changes the voltage.

Sean: If it is caued by bad solder joints would you consider it microphonics or some other kind of noise?

I remain,
Clueless...Yes microphones are made using the variable capacitor principle, but how many remember that there was once a phono pickup that worked this way too? It was called Weathers (not sure of the spelling) and the stylus movement created a variable capacitance that modulated the frequency of a carrier generated by the specialized electronics which went with the pickup. Stylus compliance was the big advantage. In the days when many pickups had VTF of 5 or 6 grams, the Weathers needed only about 1 gram, and your records would last "forever".
I have heard of this from other people that have that preamp - I suspect something in the design or constrution of it.

Call Rogue. They will tell you there is no inherent design reason for microphonics in this piece. All the tubes that I presently have in my Rogue 99 are not microphonic, and I have no problems with them. It is a matter of obtaining tubes from a source that knows how to test for microphonics and weed out those tubes. Andy at Vintage Tube, Uncle Spot, and Eurotubes will all tell you they have the equipment to test for microphonics, despite claims made by some NOS tube sellers that you cannot test for microphonics, or that all tubes are microphonic.

I think you should send your preamp to Rogue and have them comb over it for a bad component or solder joint.