OK Clif, we had a Sony CX555ES in the shop a month ago with a similar problem. The tech couldn't find anything wrong with it, the only thing he did to it, was clean the pick up and desensitize the unit and the microprocessor in case if there was some static electricity charge floating around.
Kept the unit in the shop a week on test without any problems, custumer picked it up. So far we haven't received any call back on it.
One thing I would recommend you to do is, to unplug the changer and keep it in a cool place like a basement or outside for at least an hour, this procedure usually suppresses or eliminates static electricity from the unit and the microprocessor, which could have gotten charged with static electricity by just someone touching a knob or a switch, especially if the unit is in a carpeted room. Give a try what can you loose!!
Mr.T