Mine sometimes pops when I enter certain driveways at certain speeds. If I enter the driveway at a very slow speed, it doesn't pop. I'll have to check mine some time soon, but for now, I'm driving very slowly into driveways.

 

I am having the same problem with my 07 F150. I just got the truck a few weeks ago and had to replace upper ball joints. According to the dealership the lowers were fine. I am hearing a popping noise when I back out of the driveway or pull in to driveway while turning slightly. Its not loud but just enough to drive you crazy. Im reading alot about sway bar links... is this common on fords?? I havent looked under the truck yet but will check it out tomorrow with someone shaking the truck from side to side to see if I can find it. If you move truck from side to side I can hear the same sound. Any ideas?? Thanks