I have a 2000 toyota avalon with 240,000 miles on it. I love this car! It runs great, getting anywhere from 26 - 31 mpg. Over the last year I have heard a noise like rattling metal coming from the rear of the car when I go over bumps. It has suddenly gotten MUCH worse and sounds like a bag of metal tools rattling when we drive over any bumps or rough paving. Do you know what it might be? There are no other symptoms of a problem. Thanks.