2007 Pontiac Other

Noises problem
2007 Other Pontiac Models 4 cyl Two Wheel Drive Automatic 2000 miles

I have a 2007 pontiac soltice gxp. I have just recently had the rearend differential replaced. When I turned the wheel sharply, it made a noise. They succefully got rid of that noise, but I am now left with a whistling noise, especially when I accelerate say 50 to 60 at a steady speed, when I remove myfoot from the accelorator, the sounds gets better. When I accelerate sound comes back. This is very annoying. Also the car seems to be running louder when it is first stared, than it did before the rear end diiferentail was replaced. Please help ! So aggravating this car is to new to have this problem.I
May 2, 2008.

At 2000 miles, it should still be under factory warranty. Is that the correct mileage?