1)check the bearing in the motor that carries the fan.
2)look for scraping marks on the inside edge of the removable cover, if you find
tap the cover with a ball hammer to bend the cover away from the fan ( in the marked area.)
3)slip a washer BETWEEN each screw and between the back and the inspection cover, this will have the effect of moving the cover away from the scraping fan .
wirecutterman
June 2009