Its possible that some debris found its way in the mechanism or gearing that operates the lens barrier doors when the camera powers up. I would suggest to have it looked at by a repair shop there are small springs and parts that make up for the operation of barrier doors. If your mechanically inclined and can repair it yourself with some patience, some of the barrier door assemblies can be removed at the front of the lens assembly. It may come out as a one piece unit or the doors are part of the lens barrel assembly. I have 13 years experience in the camera repair field used to see this problem on quite a few cameras, found anything from a grain of sand caught in gearing to timing being off from impact damage. Hope this was helpful for you.