CentOS - Mar 2012 - Where Did All The Noise Go?

OK, I've got 2 machines running CentOS.  One running CentOS x86_64 6.2 
and the other running CentOS x86_64 5.8.  At some upgrade point I've 
lost all sound using Firefox and Thunderbird with my Gnome desktop.  
When I bring up 'System',  'Preferences',  'Sound' and
go to the
hardware tab and test the speakers, they are working.

Any ideas on how to get the sound back?

TIA,
Gene

+ It's impossible for everything to be true at the same time +