My S60 is clapping somewhere in the back…

Hello, my S60 D5, 11.2007, 90TKM, Momentum clatters somewhere in the back. It sucks immensely. It’s nothing from the engine, it starts when the road only gets a bit worse. I can’t locate it. The seats worked, was louder – so something in the trunk. Everything looked through, got out – nothing was better! There I put the seats up again and had the feeling it won’t get quieter – but not trunk? Well my question – I used SuFu and read that I’m not standing there alone with the problem. Some write about noises from the hat rack and also roof sky behind should have called in. What did you do to turn it off? Any foam parts stuffed in somewhere, or what? Maybe I can do something with it according to the motto – error… Thanks for help Jaro