If your parking brake test kept the car from moving and it was still popping, that will rule out the bearings. You might try putting your hand on the axle while you do the test to see if you feel the joint shift with the pop. I would also suspect motor mounts and possibly struts/springs. Try opening the hood and doing the parking brake test to see if you see the engine rocking around. You may even see the top of the strut shift. ?? Hopefully this will get you closer to the cause. There were several years of tours that had problems with spring breakage. (Recall etc.)
