Defective carpet when it wrinkles up when wet. Don’t see it to often anymore. Back when they made the backing with a clay mixture, it happened a lot more and it would be really dramatic sometimes. I remember the first time it happened to me 30 years ago. Literally 2 foot high wrinkles on that old sculptured carpet from the 70’s. Now they use a polymer type of backing that still can do it, just no where as bad.