That's where I started before taking it to the shop. Removed everything from the trunk including all panels and checking the "pockets" on each side. I removed the rear seat and the front and rear door panels. My doors are quite solid now!
I have been convinced it is coming from outside and when driving past a bridge or concrete wall it is quite clear it is not coming from the inside. I had someone ride in the trunk as I drove around a parking lot with the lid open and it is from underneath the car...somewhere.
I have also removed the plastic cover the protects the fuel pump (I think) and have put spliced rubber fuel lines on and in between any area around this platic cover and the brake shields, but the rattle still haunts me!
Thanks for the replies!
01 S55 AMG Silver
01 CLK55 AMG Silver