My car has developed a noise at the rear, it's a bit like someone shaking a bag of marbles or stone chippings hitting the underside of the car. Seems to only happen when it's warmed up and seems roadspeed and load related - happens more if I'm above 50 or so and accelerating. Any ideas what it is? I can't find anything loose or any play in the driveshafts (although I am **** at finding play in UJs). Is it the diff? It's a 4 pinion open r200 - should be bullet proof I thought!