My vacuum (9-55-13) used to be real quiet but has recently become a screamer. Theere was considerable vibration with the noise so I assumed it must be bearings. I took it apart(not an easy task my first time) and the bearings seem totally fine - very solid. Then I said maybe it's the brushes. The brushes appear to be some sort of a "permanent" installation I used to love my vacuum - that's starting to fade - HELP!