What could cause a sudden loud grinding and weight shift on front axle?

What is your question?

Driving at relatively low speed, I was in the front passenger seat when suddenly there was a loud grinding sound seemingly from the front end and it felt like weight shifted from the center toward the outside under my feet. My dad checked the U-joints and axle on both sides including the axle bearings but cannot locate the issue. Now on the rare occasion that he does drive the car the grinding continues worse when starting from a full stop, and the front end feels completely instable.