Arm yourselves !!!
With a silicone caulk gun that is.
After modifying my rear door speakers by adding tweeters, of course I gained better sound performance. Since I like to listen to classical music I wanted to have a quieter car. The 2007 jeep compass has seems to have a lot of noises coming from different sources. I set out on a quest to find and eliminate them. One of the worst culprits is the plastic shields used under the wheel wells. The little plastic clips that hold them don't really do a good job of fastening those things tightly. If you knock on these shields, you will hear vibration and noise. When the car is being driven, these parts vibrate and rattle. Kill the noise by applying GE silicone with a caulk gun. You will notice a big improvement in noise elimination and reduction. Also the rear door's plastic panel make noise too. I caulked it up and voila no more rattles. If you want to go further, you can add insulating or sound absorbing materials between the plastic walls and the metal of the doors and panels. Let me know what you do to eliminate or reduce noise.
Sometime next month I will be removing my front bumper and apply silicone sealant to the black parts of the grill. I bet your grill makes a lot of noise too. I will take some photos and will post them for you to see.