Mine had the exact same thing..... Mine has been in an accident so I thought it was something serious, I looked and looked and looked. It was just as you described it did it when I shut the door and when I went over very small bumps or very large bumps. I was getting pretty fed up I had climbed under the car so much and sprayed everything I could think of with wd-40 just to try and find out what it was.. I finally talked a maintenance guy at work into driving it and trying to locate the noise. After we looked for about half an hour and pushed and pulled and went over everything we could think of with no luck.... He wiggled the HOOD!!!! and that was it..... It was the hood latch. He wraped some electrical tape around hook that the latch holds as a temporary fix and the squeak STOPED FINALLY !!!!!
I really hope this helps cause I know the feeling.....
Joe