I was driving about 35 mpg, hit some rr tracks and an awful grinding noise started that seemed to be coming from the drivetrain (transmission, axle, or rear differential). The noised stopped ten seconds later. It happened again a few days later. This time the grinding lasted a little longer (30 sec) and then stopped. It happened again a few days later. Today it happened again. This time I had to slow down to almost zero mph to get the noise to stop. Each time this has happened, the noise stopped and the vehicle ran great for the rest of the day. Anyone have an idea on this problem? (prior to this problem I had rear drive shaft u-joints installed which eliminated the clunk noise I was having when starting out from zero mph)