Paul: Thanks for the tip. My rattle is painfully present with the windows closed. I just went out and tapped on each of the center caps, just to be sure! No joy...Tom

 

Tom, check your sway bar connection to the trailing arm before you take your interior apart.

 

The source of the rattle turns out to be a large, heavy steel bushing, of the kind used to tap in wheel bearings, that had "found" its way into the left rear lower control arm. Given the mass of this thing, it's no wonder that the rattle was stupendous. I can't describe the joy of driving the 3.6 WITHOUT THE RATTLE!

By the way, the guys at Exoticars in Frenchtown deserve credit for finding it. They put the car on a lift and hit the rear tire with a large plastic hammer hard enough to recreate - and locate - the rattle.

 

WTF! Inside the control arm casting? How did that get in there?

 

That is insane. Kudos to the guys at that shop for the good detective work.

 

Paul:

If you run your hand between the top of the control arm and the bottom of the half shaft seal - it's a narrow space at the outboard end - you can feel a hole in the control arm. When the wheel bearing was being replaced, the bearing press cap must have been placed on top of the control arm, fallen in, and then forgotten. The half shaft had to be removed to remove the press cap.

Tom