I have an 2006 GXP that I bought 3 1/2 years ago with 15k miles on it, that has been making the same noise through the driver side door speaker with the car off or on when I hit bumps in the road. I figured out years ago to lightly tap of the right side of the radio in the dash, and my noise goes away temporarily, until I hit another big bump in the roadway. In addition, I have also figured out that it happens more in the summertime then it does in the winter cold months.