Hi Marioalexandro121:

I'm specifically referring to a sound that happens when the car is not moving.

Although I'm also experiencing some other loose-something-or-other noises when driving over non-smooth surfaces at low speed. I took it to the dealer. The tech there fully extended the two plastic stoppers on either side of the trunk lid - a 10 second fix. That helped some, but it didn't fix all of it. I don't know if that's the balanced way to fix it.

I think I may have to drive around with someone laying in the trunk to pinpoint the source.

Interestingly, that problem only happens at low speed over bumps (they can be slight). Outside of the stoppers on either side of the trunk lid, are there other obvious things to check?