I hear a weird noise when I accelerate, sounds kind of like something is grinding like metal on metal. Its faint but I can hear it when I am next to a car or wall. I checked my oil to make sure there was some in there, there was plenty, but it had a gas smell to it and it was black. I changed the oil about 3, 000 to 3,500 miles ago. I wouldn't think the oil would get that dark that quickly. Any suggestions would help. I have a '99 cherokee automatic, 4.0L, 4x4. Thanks.