The 350Z sphericals where the ones that Dan posted. They were brand new pieces. It's about a 50mm spherical ball, which is huge (that whole assy is 60mm OD), and they're super tight. It's not contacting anything, and it's not from the arm moving. It totally doesn't matter now. The car drives as good as ever with the SuperPro parts. I never had these problems with my S13 and a full spherical rear setup. It sounded like something massively loose, and not just a rattle. One of my brother's old S13's had inner tierods with like 1/8" of play... it sounded like that.

FS: SPL compression rod sphericals installed in arms!
WTB: stock Nismo Z suspension!