It seems to be known issue with resonator on the G6 HTCs. (G6performance. Com) Maybe because of the exhaust's size, anyway had the same problem, whistling noise under acceleration between 2000 - 3000 rpm but no other time. Checked belts, tensioners, etc, etc, no joy. No longer under warranty I had a Magnaflow 10424 put in and that fixed all the weird noise, just sounds good. Good luck!
Tuesday, November 22nd, 2011 AT 9:01 PM