Mine's been doing the exact same thing for a little while not(not too long) I had it to a mechanic yesterday. We checked everything out, and all we could find was lower ball joints, both sides, are totally shot (I said int a post a week ago that my front end was tight. oops..)
That being said, I've never heard a ball joint make noises like this, and i'm not sure if I totally believe that's the cause of the noise. The new lower control arms are going in on tuesday so I'll update you on how I make out.
It is, however, a BELIEVABLE sound - since it's pivoting on the ball joints while turning the wheel (not the wheel bearings, if the car isn't moving.)
Mine is popping during turns when sitting still or rolling slowly, plus has some vibration in the steering (it's getting worse, too.)
I'll be checking the lower ball joints while doing the driver's caliper today.
Edit: Well, you'll never guess what it appears to have been - when I replaced the hubs, I must have used the rear spindle nut on the passenger side. Yah, the hub bearing was toast. Luckily I kept the old hubs and was doing a "Just In Case" after a local shop warped the $FECAL_MATTER out of the rotor replacing four studs.
Hopefully IT wasn't warped. It took about eight passes around to get the tire snug, though - 100 ft/lbs on the torque wrench, but if it turns 1/3 to 1/2 turn, it wasn't actually at 100 ft/lbs - or it walked, one of the two. So I kept going around until it would pop immediately.