There’s always a degree of microphonics with vacuum tubes.
I have a quad of tung sol kt120’s (2018 m.d.) that are loaded with it.
Same year quad of jj kt88’s that barely sound when I finger flick them.
Im unsure how much it has to do with the “euphonic” sound of tube gear.
I always thought the 2nd order “harmonic distortion “ was most responsible for that…