Audio randomly goes mute in timeline

This post is a two part question:

I have a strange thing happening in my latest project. Occassionally the sound will mute in the canvas and/or the browser. I have not pushed the mute button. If I close the project and open it again most of the the time the sound comes back on. I'll work for a while and then it will mute again. Any ideas on why this would happen?

Also, I'm wondering if there are any regular maintenance things I should be doing to avoid curruption and save headaches down the line. I've heard of trashing preferences or locking prefences but is there any thing else I should do on a regular basis besides making sure I have the latest software updates?

Sounds like dropping out rather than muting. Have you mix down your audio? You sure audio is set to same as your audio settings in your sequence settings?