My car makes a whistling noise whenever I accelerate?

I own a 2002 VW Passat, and I just recently had my exhaust/muffler repaired after hitting a pretty good sized raccoon. Now, whenever I accelerate, my car makes a whistle type of noise. It goes away if I lay off of the gas, but starts up again as soon as I feel it shift into gear. I'm taking a small road trip this coming Monday and don't want to cause anymore damage to my baby.