The unit mutes upon uploading the system file when you go live.
I had an electrician wire and solder some in-ceiling mics on a job for us and when I pressed the un-mute button all I could hear ringing in my head was the static from the mics being incorrectly wired.

I was new to Symetrix at the time and thought it was something I did in the programming. Called support and Chris was able to call the issue just by my description. He stated the unit is muted when you go live in case the volume is all the way up or if sparky mis-wired something.

Lippa- I'm up the road a few from you. Didn't know you were so close to Woburn.