The sound was not audible by my companion pilot with a non-ANR set, or
me with the headset removed.

This fits 100% with our experience as well. ANR headphones *enhance*
hearing, and certainly cannot mask the sound of any stall horn/buzzer.
With our Lightspeed Twenty3Gs, we routinely hear things that are
completely inaudible (lost in the noise, actually) without them.

I remember a flight to OSH when we kept hearing a weird whooshing
noise. We were throttled way back to 20 squared, to stay in loose
formation with a slower plane -- something we had rarely done before.
The noise continued, and we simply couldn't figure out what it was.

After a few minutes it finally dawned on us: We were hearing the wind
as it rushed over the fuselage.

Try THAT without ANR headsets!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"