No doubt others have better ears than me... but I can't tell about the mixture by the sound while flying. I hear sound changes but think they are due more to the loading of the prop or maybe to a small degree the position of the exhaust stack relative to my ears. Nor can I detect the subtle differences in performance that come from minor over heating. Sure... grossly lean might be noted by poor flight performance but my guess is that for a lot of engines that die too lean, the pilot sensed no warning.

I've had vent lines kink and finally starve a gas engine and kill it lean and sensed no warning until the engine died.