Dial printing woes on large silent clock

Steve, I am encountering a strange printing glitch on the white layers on the large silent clock: namely the white layers print smoothly until the last few layers where it develops what might best be described as a wrinkled appearance between 8-12 oclock and between 3-6 oclock...tried twice with two different white filaments to same result...using your recommended printer settings but with the change from 5 to 4 perimeters...wonder if you have any ideas on what might be the cause? thanks Mike