might be a different pop than what i'm thinking of, but my tie-rods pop and creak every now and then under turns. at least i think it's my tie-rods, i'm actually trying to find out other causes...that's why i cam across this one. just noticed this was a fairly old post so if you have figured out what your's was let me know if you don't mind
also the bolts that hold the rack to the K-member can make a popping sound...on my car I removed them, cleaned the holes and sprayed them with lithium grease before reinstalling the bolts and that popping sound went away