This is very strange.
When I boot into F7 first time in the morning, there is no sound. In addition, the volume control applet in the top tray has a "muted" X and the volume itself is turned right down to zero.
To resolve, I go to Systems>Administration>Soundcard Detection>System Tab and here I Reload Audio Drivers.
This gives the following message:
Unable to remove kernel modules. You need to reboot your box for the changes to take effect.
After a reboot, sound is back but ONLY until I reboot again when the same cycle starts over.
What's up with this?