The upper mount carries the entire weight of that corner of the car, so to make it easier to turn the steering, there is a small ball bearing ring in it. Dirt can get in it, or the cage that holds the balls can crack. The rubber center part of the mount can deteriorate too. That will allow it to settle so the body sheet metal drags on the mount.
You have to listen for where the ratcheting noise is coming from while a helper turns the steering wheel, but the upper mount can do that if the balls are running over dirt or part of the cage. The thumping is the extremely common complaint caused by the wound-up spring snapping free and turning.
The rack and pinion steering gear can cause a ratcheting or rumbling noise too, but that is much less common. Typically by the time it gets that bad, you've had a power steering leak for quite a while.
Wednesday, November 11th, 2015 AT 11:18 PM