Is there a name for the sound produced by the mechanical action of a musical instrument? I'm referring specifically to sounds not usually associated with the instrument's voice—the movement of a trumpet's valves, the hiss of a trombone's slide, the clunk of a piano pedal being engaged.
I've always considered the rhythmic clacking of the saxophone keys an essential effect of this Philip Glass recording (Concerto for Saxophone (Quartet Version) - Movement I, off the album Saxophone from 2002):
And I believe it is being used quite intentionally in this Balmorhea song (To The Order Of Night):
I sometimes, analogously, call this effect "pentimenti"—a visual arts term, referring to the not-fully-obscured remnants of previous stages of a painting or drawing.