Tube preamp noise


I acquired an all tube preamp, and one thing I immediately noticed was that the preamp is super sensitive to any external impact, however small may it be. With a gentle tap on the cover of the preamp is echoed and heard on the speaker even when the volume is set to minimum. Same thing when I tap on the audio rack, other equipments (power amp, cdp, turntable), and even on the floor.
It is just like the sound you would hear from the PA speaker when you tap on a microphone.
Is it common on certain preamps?
Anybody experienced this?
128x128ihcho
It would help to know which particular preamp you got and what types of tubes it uses?

Some types of tubes are more "microphonic" than others. Other times it's just a bad tube and a replacement is all that's needed. Beyond that, it's the implementation or construction of the component.
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Many thanks.
I will try to find a bad tube. Well, one of my friends is a strong bias on tubes and almost forced me to buy a tube preamp when I was about to upgrade, but I am not new to tubes. I may be forever like that. ;-(

Anyway, thanks for your help. My preamp uses 6SN7.
I will try to find a bad tube and replace with another, and see if the problem goes away.