Candy it's a bit unusual for a ferret to not be frightened of a big
vacuum cleaner, but it happens.  Your ferret might love the smell, or
the feeling of vibrations it puts out.  The way it moves around back and
forth on the floor could be enticing to chase.  So that isn't a sure sign
of your ferret being hard of hearing.  It's what I'd call a "red flag" to
indicate that you should investigate the possibility.
 
I have a page that lists all sorts of ideas on how to home test your
ferret for deafness.  Go give it whirl:
http://wolfysluv.jacksnet.com/test.html
 
Wolfy
http://wolfysluv.jacksnet.com/
[Posted in FML issue 4949]