IIRC, before 9/11 there was a major increase in chatter.
Hamilton said Sunday that there was "a sense of urgency" in the U.S. government in the summer of 2001, when U.S. intelligence began picking up extensive "chatter" from terrorist suspects about an imminent attack. But Kean said the administration "let down their guard a bit" just before the attacks when the chatter subsided. And most U.S. officials believed the threat was overseas.
"There's no question about it," Kean said on Meet the Press. "We were not at the state of readiness on Sept. 11 that we'd been (at) back in August. ... I think when the chatter went down, when they didn't hear all these people talking to each other so much, there were other priorities out there."
So, I don't agree that the lack of chatter can unambiguously be attributed to success in the War on Terror.