I have had the Explorer at the dealer twice for warranty coverage or recall work. They have not been able to replicate this intermittent problem while in the shop, however it does occur a couple to a few times a week. There are three memorized seating positions. When you select one of them, the mirrors, seats, pedals and steering wheel are supposed to all adjust to the saved settings for the driver that saved them. Sometimes the side mirrors wander off to the far right/left/up/down extreme and then start making popping sounds. I assume they are trying to adjust beyond limits. Sometimes they will recovers and moves back where it should be, other times they just stop while adjusted wrong. Occurs mostly on the driver side mirror, but it does occur on the passenger side as well.