This is a picture of the rear subframe and floor. The grey stuff is structural foam.
This is how I found the car after a BMW dealer boot floor repair.
I removed the foam ( bell metal ) myself as it is bridging the subframe bush and anti roll bar.
I don't want to bad mouth the repair but this should have come back to me like this ! This photo was taken nearly 12 months ago but thought I'd share . Check your cars people !