Hi Tim, we have had loads of rattles too in the first month of having the DS. 2000miles done, I'm a high mileage driver.
Rear seat, fixed by a generous amount of anti rattle tape between the rear of the seat and the plastic behind it. LR had fitted some already but it had worn through
Seat belt. constant rattle at the seat belt mount as you described. panel wasn't fitted correctly, just held on by the door seal rubber!. replaced and refitted by the dealer so gone now okay on both sides.
all the seat belts rattle against the side plastics when they get stuck down the side of the seat, caused by the plastic clip on the seat belt. fixed by covering it with anti rattle tape. it would have been better if LR allowed the buckle to go all the way to the top out of the way.
Rattle in engine bay, battery cover not secured, fixed by dealer
Rear boot cover, just plan poor quality. strengthened a bit to stop flexing using pvc interior trim along the metal edges and anti rattle tape again where plastic meets plastic, but the best way is just to take it out the car.
LR have just used some pretty poor materials in places, but thankfully between the dealer and myself I've managed to get rid of them although I do still get the odd rattle and have no idea were its coming from.
on top of the rattles also had, A/C failure, wheel alignment out and bonnet hitting headlamps because of no bonnet stops being fitted and three trips to the dealers. LR needs to up its quality control. hope the 2016 model is much better.