Had this same problem, it developed into "pops" or "creaks" when turning on rough roughs, speed bumps, normal turning(body roll) etc, it would even do it with the car off sitting in the garage if I turned the wheel between say 11 and 1 o'clock. I think brought on by my driveway, I have a "bump" type entry, dont have the regular square edge type sidewalks.. its a pretty aggresive bump while turning "sharply" inot the driveway.
I had the car at the dealer 2k before the warranty ended at 76k for it and they did the following:
new tie rods
new sway bar links and bushings
they throughly spray lubed (silicone I think) every joint except the str rack bushings
I got the car back and the noise was pretty much gone, sometimes there will be a slight "pop" which seems to happen most in the morning as im backing out of the garage after the car has settled overnight. I have the poly str rack bushings, just havent put em on yet.. this is where I think the problem is really at, if your car will make the pop noise from turning the wheel while not running have someone do it for you and get under the front of the car, I did and it seemed obvious it was the rack bushings.
There is a tsb for this to replace the str. rack bushings from Ford.