I had this problem start a month and a half ago and I could use a little help diagnosing the problem. First off the vehicle is a '00 Silverado Z71 extended cab with power locks/windows. Initially when I would unlock the doors, either with the key fob, or switch on the driver side door the passenger side lock would sound like a "machine gun" and would make several quick clicks in a row, where the driver side only makes one. About three weeks after that started the door (passenger) would not lock anymore. The slider(?) on the door panel indicating the door being lock/unlocked would attempt to slide into the locked position but would then slide back into the unlocked position. The other day the door started locking again but still makes the machine gun sound when unlocking. I first thought it might be the lock actuator going bad, but now I'm not so sure. Does this sound familiar to anyone? If it is the actuator, the only place I can find the one I need is a dealer, and I really don't want to spend that much money.