Rattle noise from Trunk, 04 SS

Hi
I have posted this numerous times of various sites. I am still looking to see if anyone has a similar issue. When I drive on an uneven road surface, i will hear a rattle either from the trunk or rear of car. The dealship has had the car twice and they can not find the source. The length of the sound depends on the length of the uneven surface. The noise is driving me nuts. Not so much that fact that its a rattle, but the fact that we can not find the source. Does anyone have any idea's or similar problems? I drove with the rear seats folded down and I was able to get a better hearing for it, but not a clue as to which side/area it is coming from.

Thanks

I have the EXACT same problem!
Depending on the surface it's a strange noise like someone banging the body whilst in the trunk a some what mid pitched 'dunk' noise!
Like you, I cannot seem to find the source.
Except I have a 95 Monte LS.
I thought it was the bolt holding the shock in place located at the top of the wheel well, however this was not the case.