Originally Posted by andrewwynn

You only need to replace if they fail. The primary symptom is a loud Humm sounds a bit like the sound of a prop plane in the movies. Will get louder and louder as three initial defect propagates. Often not always the defect is deeper in one piece so you will get a wuh wuh wuh sound I refer to as UFO sounds. It's usually easy to tell a bearing has gone south but you may need to enlist the help of an indigenous tracker to figure out which corner because the sound travels into the frame of the car and goes literally everywhere.