I just bought a 2004 XTERRA. I love it, but I noticed today that when it's in park, an odd noise comes from under the main body of the car - does not appear to be coming from the engine. I am having it looked at tomorrow at a Nissan dealership, but before I go in I thought others might have had the same problem.
It is not a clicking sound as much as a patterned, low, mechanical sound. It is sporadic. The car has 54K on it and runs beautifully (including going in reverse).

Thanks for your insight!