59rkg43GS4

I have the same clunking. On level ground, hold the brake, put into drive, followed by reverse. You will hear it. I didnt have the issue until I went and changed my Lower Control Arms. No2 to be exact. Clunking got worse, it was bad over all the small little rocks in my driveway. Checked the bolts on the Arm and they had gotten loose, and were loose enough to be turned by hand. Put loctite on them and tightened back full. So far havent heard it but once, I think its something else now.

Id say check those two bolts

Im going to check my strut to see if maybe that piece you were stating has shifted .