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 since. Tightening the cover screws back to TIGHT hasn't helped. Any suggestions as to dampening materials for the cover? Not familiar with modern materials. Thanks!