The balljoint is a likely culprit.
When the wheel is off the ground, the spring applies all of its (significant) force towards pulling the balljoint upward within its socket.
This means that you would not observe any lateral play in this state, and the groan is likely to go away. (Note-If you had a MacPherson strut, you could indeed diagnose a warn balljoint in this manner, because there would be no load.)
When the wheel is on the ground, the weight of the car forces the balljoint down into its socket, which may be the state where it groans within its corroded socket (mine were like that).
You can diagnose a worn balljoint by jacking under the control arm until the tire leaves the ground, and then check for lateral play by grasping the top and bottom of the tire an attempting to rock it inward and outward.
Ideally an assistant would do this while you observe the balljoint for play.
Another method is to observe if the balljoint moves upward at all (the gap between knuckle and control arm increases) as you jack under the frame.
Could still be in the steering rack though, since the noise may go away without the extra 'load' of turning the wheels on the pavement.
1986 300E 5-Speed 240k mi.
Last edited by csnow; 06-12-2002 at 10:57 AM.