Here's the video I got of one of Tinley Park's Thunderbolts I think set to chopper level 6. AFAIK, all the Tbolts are dual-toned and are slowly being replaced when they break down with 2001s.
This one sure sounds healthy to me! I didn't think it was going to go off as it was a minute or two late, but it did and it scared the living daylight outta me! 3 minutes of attack, then 3 minutes of alert.
http://www.youtube.com/watch?v=CyT4k_jpMPc