Make sure you retorque your plugs after changing. I changed mine about 200 miles back and torqued them to 18 ft lbs. When I checked them this afternoon, #2 was loose by 1/4 turn and #1 was not much better. If I didn't check them there could have been problems in a few miles. Every thing is fine now with the re-torque set to 20 ft lbs.

 

Although I've always been reluctant to tell others to go against the recommended torque, I've screwed my plugs in to 20 lb/ft ever since that plug recall came out. They've never loosened.