I bought my 2007 G6 a week ago and when I test drove it, I heard the whistling noise in the exhaust when I would accelerate beyond 2000 RPM. I started not to purchase it because of that and the fact that the salesman said, "sounds normal to me". So, I came home, searched it out and found this thread. I decided to go ahead and buy. I ordered the Magnaflow 10425 from Summit Racing for $68 and paid a local muffler shop $65 to install (GM dealer didn't want to use my parts). It is fixed and sounds great now! Thanks! By the way, the car was priced $3,300 below value- that could have been how I got it so cheap!