I have a 20' above ground pool - approximately 4 years old. About 2 weeks ago I noticed that on 1 section of the liner, wrinkles have started to appear and that the liner itself bumps out a little more toward the top of the pool than in other sections. The wrinkles may have been there before, but I have never noticed them. Seems that a few extra wrinkles have appeared in the past few days. Should I be concerned ? How do I correct or do I address when I get ready to close the pool ?