That was sometimes a problem with the CB1. I recall Theta had a chip upgrade to alleviate that problem, which would mute for say a second when you turn on or change audio source.
But CB1s are way out of warranty now. And I doubt Theta has chips to repair the CB1 anymore, but its possible.
But you can pay to upgrade it to the CB2 or to the CB3. The CB2 is a big improvement functionally and sonically.
If you bought it used recently, hey, your seller should have warned you about the problem. Because it should have been fixed back when the unit was in warranty.