It's the guide rod joint, or track rod mount. It's a ball joint attached to rear of the guide rod/track rod. It's about $60-70 or so I think. It's really pretty easy. Check the DIY section, there's a complete write-up on it there. Might as well do both while you're in there. You can actually pull and repair it without compressing or removing the coil spring, but be advised the spring will push the control arm backwards, and you will need to push it back forward pretty hard to replace the guide rod. Just have a friend too help.
And, yes, the major sympton is a clunking over sharp bumps, especially with the brake lightly applied.

DG