Why can we hear the sound of the ocean in some sea shells?

[Lacy33]

How is it one can hear the sound of the ocean in some sea shells?

 

[matthyaouw]

http://www.howstuffworks.com/question556.htm

 

[brewnog]

It's because every sea shell contains a tiny radio with loudspeaker, tuned into the national seaside acoustics organisation's transmitter.

 

[Lacy33]

It's because every sea shell contains a tiny radio with loudspeaker, tuned into the national seaside acoustics organisation's transmitter.

LOL,
Well there you have it! I didn't think actual nature had anything to do with it. I'm so happy I asked someone one smart... Realllllllly smart!~

However reading from the link matthyaouw offered, I tried holding my hands over my ear and did get such a sound but only on the side of the desk that has a fan. The other ear does not get the ocean (just gremlins) I guess my right ear is receiving transmission better right now.
What this does not explain is being in total quiet and hearing the sound loudly from a sea shell. Unless there are noises that have that rushing sound going on all the time and we just don't notice it.
Want more information please. This came up in a conversation because I got a sea shell many years ago as a girl on Valentines' Day. But now everyone in our home is watching this thread.
Thanks