if you found a dealer here in SD that said you should be fine with mods, I wanna know who they are haha! Maybe the sound was there all along, and you're just noticing it now? These LT1's are noisy AF.
Be sure to record the sound you're hearing before you take it in, just incase they don't hear what you're talking about.
Also check out this thread, and compare:
http://www.camaro6.com/forums/showthread.php?t=506235
Maybe even add your recording to the collection.