Great find Jeff:
Hoover used a felt pre-motor filter than can only be accessed by removing the cloth bag and trim (four screws). You can then access the filter to clean it. There's a brass brad that holds the filter to the motor's fan case. Be careful not to dislodge it when removing the filter.
I never understood why Hoover would make the filter so difficult to get to, so much so that the average person didn't know it had one. Every time the bag 'snaps' back after pressing the lever on the bottom, some fine dust is released into the bag housing. That dust, along with whatever dust leaked through the cloth bag, is lodged on the pre-motor filter.
