Mine since new in I think 1989.This has happened intermittently since I got them- the dealer (George Merrill of turntable fame) gave me some sound deadening sheets which I used for years (with bricks) but have lost. I took off the cover to inspect the caps and components and it seems worse...
My much loved Sequels have developed softened paint over the years- you can drag your fingernail through it and leave a mark. I called Jim Powers and he said they had some bad paint back then and he recommended disassembling the speakers, stripping them and repainting them. However, he didn't...