2003 Buick Century, the rear end of the car has developed a rumbling/
rattling sound when driving over rough pavement, especially at slower
speeds. On smooth roads, there is no noise, and I don't notice the
noise (as much) on rough roads at "non-slow" speeds. The driveability
of the car is not affected. A mechanic lifted the car and did a visual
inspection, nothing obvious jumped out to him (signs of rubbing,
something loose, etc.).