sound mutes automatically

Re: 4x2.5 GHz PowerPC G5 OS X 10.4.5

The Output Volume mute button in the Sound window of System Preferences automatically mutes itself on a regular basis.

Does anyone know why this is happening or how to stop it from happening?

Thanks in advance.

Do you have any volume control widgets that you may have stuck in mute?
Any sound programs running? (ie Garageband, Soundtrack pro, Audacity, etc.)

The only widget I have with sound is iTunes and its mute is not activated.

I do have Audacity, as well as Quick Time, WMP and RealPlayer. The mute options in all of these programs is not activated.

I don't use GarageBand so I removed it from my dock earlier. Now, wanting to open it up and check out its mute options, I could not find it within the applications window. I may have deleted GarageBand but I don't recall doing so. Maybe its worth re-installing GarageBand in case its the problem area.