My 1998 Volvo C70 rattles when I go over rough ground. It sounds like I am towing a boat trailer without a boat, a metallic sort of rattle. I thought it was either a muffler bracket or a loose anti-sway bar, but apparently it is not. It sometimes disappears. I thought it might disappear when the car has warmed up, but it is not consistent. It’s driving me crazy! It definitely sounds like it is coming from the rear wheels or suspension as when the front end goes over the rough spot, it is silent.