My Crosstar last week developed an irritating noise from the back when going over uneven road surfaces.
I check for anything loose in the boot, found nothing and then looked at the retracted seat belt for a middle rear seat passenger.
Next to where it comes out of the head lining there's a little slot to accept the loose bit that goes into the fixing in the seat when in use. I just pushed it in and it locked. It was this end of the seat belt rattling which was causing the noise.