Like I said I had the same problem with that exact same clunk you described while backing up with the wheels turned to the right if I remember correctly it would also grab every rut in the road it was a handful to drive to say the least. It was a loose steering box. I didn't figure out what it was until it was almost too late one of the steering box bolts was gone and the other 2 only had a couple threads holding them in. You need a 3/4 inch socket and I think a 6" extension I didn't even need to jack up the car to check them or tighten them.