High pitch whistle on acceleration

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!

Sorry everyone, on my post, I typed the part # in error, it was the Magnaflow 10424 that fixed my whistling noise also!

I live in the sticks where the closest Midas is like 60 miles away so I had to go to a privately owned muffler shop to get mine fixed. I showed up at 3:30PM and they put it on the lift and told me that "due to the bracing, it would take a while and they didn't have time to get to it that day and to bring it back the next day". I took it back the next morning and left it, then picked it up that evening and the labor bill was only $65, of course that was a private owned place and not a franchise. They did have to remove the bracing on mine and they actually showed me how there was no way to get to the resonator without doing so. I didn't see any way to. Mine is an 07 convertible. The price for me wasn't that bad, just an inconvenience of not having the time to wait on them, I had to get a ride to drop it off and to pick it back up.