My 2000 GMC Safari van clunks and jerks when I stop or start. And does the same when I turn the wheel all the way either direction.
Difficult to guess without some testing. I would recommend placing the front end securely on jack stands. Turn the wheels from side to side to try and reproduce the issue. Inspect all moving components. Look for loose ball joints and wheel bearings while still listening for clunks. Wiggle the tire from top to bottom and side to side while someone looks for anything loose.
With the vehicle on the ground, in park and the engine running turn the wheel all the way in either direction. Doing this should help recreate the issue and allow someone on the outside to listen for the problem area. Once the area is located a more in depth inspection will be necessary.