Heh, so what if they can hear you...you giving vital information to your teammates has a much greater value than keeping silent because the other team can hear you relay vital info to your teammates...
Now if you're talking near the flag on sudden death and you teamtalk saying "I'm near the flag at location X, I'm gonna extend sudden death!", that would be a mistake
Now if you're talking near the flag on sudden death and you teamtalk saying "I'm near the flag at location X, I'm gonna extend sudden death!", that would be a mistake