I get this regularly, and usually when my caller is on a cell phone. It seems to me that either cell phone static (noise on their line) or some sort of CODEC renegotiation triggers it. Usually my side of the call turns to nothing but static noise, but the other side still hears me.
Often times a caller will accuse me of having done something to trigger this very powerful and useful feature of Google Voice (such as to keep note of details that I cannot write down where I am at the time) and refuse to call back.
It also seems to be the same people who never answer their own phone who are most offended when this happens, so one is dependent upon their return call.
Since there is no way that I am aware of for Google Voice to trigger this behavior of theirs on outbound calls from my Obi device, there is no actual solution or way to avoid it from happening until such time as Google Voice decides to address the matter.
I have been hoping that someone from Obihai / Poly, obviously with good communication with Google, could bring this matter to Google's attention.