http://www.camaro5.com/forums/showthread.php?t=416609
Tried over in the Camaro issues with no luck maybe someone here might be able to chime in. I removed the heat shields on the stock headers and the sound was still there today. I don't know if its normal as I remember my LS1 Valve-train just being loud like a sewing machine maybe perhaps the LS3 is just as loud when going through the rpm's. About 10secs into the video is when I shift to 3rd and you can hear the flutter I am speaking of.
http://vid157.photobucket.com/albums.../VIDEO0008.mp4