One problem related to noises during shifting has been reported for the 2004 Chevrolet Trailblazer. The most recently reported issues are listed below.
Purchased new Trailblazer in may 04. When vehicle had approximately 3,000 miles on it, I started getting a rattle or loud buzz when accelerating at approximately 25 per hours just before the vehicle shifts. Occasionally, the shift if jerky. The vehicle has to be warm and the rattle or buzz first manifested itself after I turned right and accelerated from a stop. When warm, this sound is repeated almost every time I turn right and accelerate. When warm is also occurs when I just accelerate from a full stop. Occasionally, it will also occur after a tight left turn. I reported it to the dealer and they told me the computer did not show anything wrong. On the second trip to the dealer I reported it again. Still no fix. The noise is very annoying, but I cannot tell that it is doing damage. I certainly would not have bought this vehicle if it made this noise on the road test. I am estimating the rattle or buzz sound has occurred at least 75 time to date.