I’m compiling a list of great jazz pianists that moan when they play. I wonder if it’s a stylistic choice, or some artistic savant thing that trips when you hit a certain level of genius. Anyway so far I have:
Erroll Garner
Keith Jarrett
Oscar Peterson
Bud Powell
Though not a jazz pianist, Glenn Gould is, of course, best remembered for his technical virtuosity and his adding an extra, moaned/hummed, line of counterpoint to Bach pieces.
Lennie Tristano. Never heard it when he’s with a rhythm section, but it’s audible in solo piano recordings (“The New Tristano”)
Keith Jarrett explained his noises in “The Art of Improvisation” (a DVD made about him). He said that at a certain level of involvement in the music, when things are really clicking with the band and within himself, there’s no way to NOT make a noise.