Resonating rattle at slow speeds

[DGW67]

Hi all

I have a slight rattle from the rear of my Continental GT, only at slow speeds on uneven surfaces but I’ve been through all parts of the boot and trim and can’t see anything obvious.

Does anyone know of there are any common issues with this model that can lead to rattles? Or can somebody technical suggest where I should look? The car is a 2016 model Speed.

Thanks in advance