We had a regular clicking/ticking noise that was driving us crazy. No article on the internet addressed it, and it would come and go erratically - I could never get it to make the noise when I pulled the refrigerator out and searched. That turned out to be an important clue - my wife finally spent $120 to get a repairman out, and it turned out to be a warning label on the power cord being blown by the exhaust fan against the back of the unit. He said he'd seen that happen a dozen times. I'm putting this here so others can avoid the same facepalm moment.