That can actually be caused by the strut mount, the ball joint, or the sway bar end link. Any load bearing device that moves when the a-frame does. In my experience, it tends to be the ball joints but not always. I is almost as likely to be the strut mount.
My Taurus had the same problem (there is a TSB for it I think) and my ex-wife's Turdstar did as well. I suggest that you get a grease gun if you don't already have one. Then purchase the syringe/zerk fitting attachment.
To grease the problem child...
FIRST: Yes, you would want to set the brake just in case your ex-wife pops it into D.
1. Turn the wheel all the way to the left and lay down in front of the left wheel.
2. Stick the syringe fitting into the lower ball joint and sauce it up until it leaks out.
3, Then hit the outer CV boot (mine took 12 pumps with a full-size grease gun), inner CV boot, sway bar boot(s) and tie-rod end.
NOTE: The syringe will be tough to get through the CV boots.
4. Repeat on the other side.
ALSO NOTE: My sway bar boots were gone but I still managed to get some grease on the joint. I'd also spray some lubricant in the sway bar mount bushing area (the rubber blocks that capture and mount the sway bar itself). I'd avoid WD40 since it tends to evap within a few days.
A BETTER WAY: It's also better to jack up the car by the center of the k-member and grease the joints unloaded; turning wheels side to side after you do it. Set the brake because it's best to turn the wheel side to side with the car running. If it isn't running when you turn the wheels the rack will push fluid through the PS return line, which can overflow the PS pump filler cap vent. It wouldn't hurt anything, just make a mess.