Gary, Hi. Actually, I have. We had a room-size anechoic chamber at my
grad school. It's quite an experience to sit in one, on a grid of wires,
while this huge door is closed and the lights are turned off. At first
all you can hear is the blood coursing through your ears - a loud
pounding. As you relax, and your heart beat slows, you can hear white
noise between the beats. I don't know if this is from Brownian motion
(that's what someone told me!) but I would love to repeat the experience
with shells and cups. It seems to me that the shell noise is always
louder when the ambient noise is louder, which would support your
explanation. I'd forgotten your article - I'll dig it out. Thanks.
  Bill H.