[piper6909]

The other thing I can think of is something is going on inside the differential. Since it doesn't do it when it's jacked up, the only other suggestion would be if you have a friend at an oil change shop. They have those pits you drive over and a guy is inside the pit underneath the car. See if they're willing to let you or somebody drive it back and forth while somebody's under there listening. The problem with that is that there's the damn plate underneath that covers everything up. I don't recommend driving that car with that thing off, as it's also a structural part.